Power of the Sun

As I eluded to in my last post, there is one project, or upgrade, that made the list along with the repairs, and it is something that I had wanted to do since before we built the hardtop. When Doug, my crew that came to help out with some of the repairs on the boat, came up with a system that wouldn't cost too much more than the fuel I anticipated we would use with the generator on the trip (at Bahamas prices), I decided it was a worthwhile investment.  I'm, of course, talking about adding solar power to the boat.

No, this is not my boat.

When I was designing the hardtop, I intentionally moved the sail viewing window forward just a bit in order to allow for the larger size panels you often see in residential applications as well as building in wire chases that could be used for solar.  At the time, getting panels for around $1 per watt was a very good deal.  Now the power output has increased and prices have fallen and you can get 320 watt panels that should put up with the marine environment for under $0.60 a watt.  He also found a MPPT solar controller that was getting pretty good reviews for $150.  A couple lengths of 6 gauge wire from the controller to the batteries, the special 10 gauge wire for hooking up the panels, a couple breakers, a wire gland for sealing the wire chase hole in the hardtop, a special tool for installing weatherproof MC4 connectors on the wires, and a couple other odds and ends for installation and I'd get "free" power from the sun.  Since Doug would be passing nearby the solar panel supplier on his way to the boat, it would also save me the (not insignificant) shipping cost for the panels.  The whole system would end up costing me around that magic $1/watt number that used to be reserved for just the panels.

The first step in the process, after getting all the materials to the boat, was to drill new holes in my beautiful hardtop.  Having worked so hard on that top, I had mixed emotions about drilling 5 holes for each panel in it...but if I wanted solar it had to be done.  We brought one of the panels to the boat, attached the mounting brackets to it, and marked the four mounting hole locations for each panel.  We carefully determined where the middle of the wire chase was on the underside of the top and marked the larger hole for the wire chases.  Using my drill guide, I drilled oversized holes until we reached the bottom fiberglass skin, cleaned them out, filled them with epoxy (the top is foam cored, so I needed to create a sealed "sleeve" for the holes that would also act as a compression post to tighten bolts), and drilled the smaller final size hole at each location.  It all sounds simple enough, but this is a boat project so we had to fight weather, wait for epoxy to cure, as well as other issues so making the holes ended up taking 3 or 4 days to complete.

Carefully locating the center of the wire chase.

While waiting to complete the holes in the hardtop and get the panels mounted, we installed the solar controller, breaker, and wiring from the controller to the battery bank.  The solar controller and breaker were mounted in the engine room next to the original battery charger for the boat. The wiring was run from the large main bus bars below the main electrical panel (think of a bus bar as the extension of the positive and negative posts of the battery bank), through the breaker, and on to the controller.  The controller connection was another interesting problem to solve.  Our calculations showed that we should use 6 gauge wire for the charger, but the charger terminals would fit at most a 9 gauge wire (remember the larger the gauge number, the smaller the wire).  Since the controller is rated for 60 amps, it has two connectors for each of the positive and negative battery outputs and the instructions said to run two wires to the battery...probably done to save in production costs of the charger.  Well, I didn't want to double up wires. It turns out if you take a 6 gauge wire, strip off the cover, divide the wire strands in half, and re-twist them into two conductors you end up with two 9 gauge wires.  So, that is exactly what we did to the end of the 6 gauge wire cable.  Marine grade wire cables use thin diameter strands of wire for the conductor (for added flexibility) so it was a fairly easy process. Seal it all up with quality adhesive lined heat shrink tubing and viola, a custom single cable that hooks up to the controller. A few zip ties and zip tie mounts and the cables were installed.

Drilling and filling holes in the hardtop.

Once all the holes in the hardtop were ready, we mounted the solar panels and sealed the top sides of those holes with butyl tape.  We then used an electricians fish tape to pull wires from each of the solar panels through the unsecured gland boxes, the chases in the hardtop, and to the access panel in the top corner of the targa (arch at the rear of the boat).  There we used two Y adapters to connect the solar panels in parallel and ran the resulting single set of wire down the rest of the arch, into the engine room and over to the controller.

Making the custom connection wires.

After wiring the controller up, were now ready for a test.  Of course, we were ready at about 5pm and the sun was a short time away from setting, so this wouldn't be a real test of power generation, but it would be enough to verify everything is hooked up and working.  We flipped the breaker on the battery connection and the controller came to life and recognized it was connected to a 12 volt battery bank.  A few parameters were set in the controller and then the solar panels were connected.  We have power generation!  It was only about 150 watts coming from the panels and a couple amps going into the batteries (I don't recall the exact numbers), but it was proof that the system works.

Solar controller mounted next to the original charger.

The next day we did a second test.  It was fairly sunny and right around noon and....wait a minute.  It was only showing 150 watts from the panels and under 10 amps going into the batteries.  Oh yeah, need to turn off the regular charger and drain the batteries a bit...it was doing a constant voltage topping charge because my regular charger was taking care of the batteries while I'm plugged in at the dock.  I used the inverter and a space heater to pull some energy out of the batteries and then tried again.  That's more like it.  Even with the boat sitting so that one panel tilts a bit north and the sun was at best about 45 degrees from overhead, we were seeing 460 watts coming from the panels and 31 amps (at proper charge voltages) going to the batteries. Yay!

Data from the Android App.

I finished tidying up the wiring and checked the connections with my non-contact thermometer to make sure there wasn't any resistance causing heat build up.  We then reinstalled all the access panels and I glued down the wiring glands on the top so it is again waterproof.  The only thing left to do on the install is figure out some sort of skirting for the panels so lines don't accidentally get hung up under the panels.

Panels Installed except for line deflection skirting.

In the days since the initial install, I have run a number of other tests and found that, as long as I'm not running electric heaters or air conditioners, the setup seems to keep the batteries charged.  Of course the real test will be sitting at anchor when I have to use the inverter (or...shudder...the generator) for 120 volt AC service. 

I also found a glitch in the solar controller.  It was rarely going into its float charge state.  I contacted their technical support (which only seems to be available via e-mail) and found that the charger has a hard coded value for the switch over point from topping charge to float charge and doesn't take into account the recommendations of most of the battery manufacturers or size of the battery bank.  For most solar installs that have loads that take power most of the time, this isn't really an issue as charging time is limited by sunlight hours.  The only time it comes into play is when the battery is fully charged and there isn't a load (like a boat in storage). I was informed that, at the price point of the charger, the manufacturer would not change the programming of the device to better align with the lead acid battery manufacturer recommendations. Fortunately there is an easy work-around by simply setting the controller to limit the charge voltage to the lower values used for float charging when the system isn't actively used.  With the WiFi feature of this controller, it is easily done.  Not the ideal solution, but good enough for my purpose.

Overall I'm happy with the result.  One of the things I really hated was to have to start the generator in an otherwise peaceful anchorage in order to recharge batteries.  With this addition, I hope I won't have to do that very often.  Not having to burn fossil fuels in order to produce energy is also a good feeling.

Finishing the Battery Install

Bet you thought I was done with this task back in Southport.  The batteries have been installed and functioning for a while now and everything seems good.  But there was one last thing I wanted to accomplish.  Making future maintenance a bit easier.

One nice thing about our old battery bank was it consisted of 3 sealed AGM batteries.  Basically they are the type of batteries once coined "maintenance free". As long as you kept them properly charged and didn't kill them or overcharge them, there was no real ongoing maintenance (although periodic inspection is probably still a good idea).  Switching to the golf cart battery bank, we went away from those convenient sealed batteries to ones that require periodic watering.  Already having far too much to do on a boat, adding this complex maintenance task was the down side of this approach.

Now, you may be asking yourself how checking the water on the batteries could be that complex...or wondering if I finally lost my marbles.  Here's the deal.  To check and add water to the batteries the way they are I would first have to dig all the stuff out of the locker above the battery compartment. Then I would have to remove the false floor to the locker that acts as the battery compartment lid to reveal the batteries.  In order to access the caps to the batteries, I would have to loosen all six of the hold down straps keeping the batteries from bouncing around while we are in motion.  Then, finally, I could check and, if needed, somehow manage to pour just the right amount of water into each cell siting deep inside that locker.  Once that was complete, I would have to replace all the caps, refasten all the hold downs, replace the battery compartment lid/locker floor, and finally put all the "stuff" back in the locker.  Doesn't sound quite so simple now, does it?

Fortunately some folks that make batteries for larger battery banks or battery accessories came up with a solution. There are battery watering systems out there that make the task a bit more manageable, particularly when batteries are not so easy to access. The down side is that some of these systems can get a bit pricey. You can find systems that are fully automatic where you just need to keep a reservoir full of distilled water and the system will fill cells as needed.  For a little more reasonable cost, there are systems that are semi-automatic where you use some sort of pump to periodically pump water into the system to fill any low cells.  After much scouring of the internet, I found a reasonably decent price on one of the latter and ordered it soon after arriving at Hammock Beach.

The system I found was the Flow-Rite Pro-Fill 6-Volt RV edition. The best price I found was at RVUpgradeStore.com (a boat is just a floating RV, right?).  The 2-battery kit was $44.70 and the pump was $18.03 at the time of purchase.  This made the whole system for my 6 batteries come out to $152.13 (with free shipping). Well worth it if it can make the bi-monthly task of watering batteries go from the above description to a 2-minute fool-resistant job.

The battery watering system and pump

How the system works is pretty straight forward. You replace the caps on each cell of the battery with the special ones in the kit.  These caps have a connection for a water supply tube and are equipped with a float that hangs down into the battery cell.  You connect all the caps together using the water supply tubing. As water is supplied via the line, the cell fills up until the float closes a valve in the cap, stopping the water flow.  This is supposed to keep the water in each cell at the proper level without having to even look into the cell.

The kit arrived yesterday, and since I hadn't yet done any maintenance on the batteries, it seemed like a perfect chance to install and test the system.  Of course, to install the system, I had to perform all the steps I outlined above in order to remove the old battery caps.  I then installed the new watering system battery caps on the batteries and connected the water tube flexible manifolds to the caps (some of the old literature claimed there were both flexible and rigid manifolds, but the kits I received only came with the latter). I cut some of the tubing and connected each manifold together and attached the filling port to a central location in the system and ran it to an opening in the battery box lid. I finished by taking the supply of red rubber caps to plug all the unused manifold connectors.

The pump for the system is a simple squeeze bulb that you are supposed to dip into a jug of distilled water. The instructions say the jug should be below the top of the batteries to prevent siphoning.  I'm not sure if this is really necessary, but the water jug fits nicely into the locker besides the battery box which puts it at the same level as the batteries and makes a nice storage location for the jug of water right next to the filling port.  I hooked up the pump and dropped it into the jug and gave the system a try.  A few squeezes of the pump ball and water was flowing through the tubes.  When the ball could no longer be squeezed it indicates that all the cells are full and the valves in the caps closed to prevent overfilling of the cells.  I disconnected the pump and let the water drain back into the jug.  I then checked a couple of the cells and, although they were not that low to begin with, they do appear to be at proper levels.

Watering system installed.  Lots of black tubes and wires now.

Next time I need to water the batteries, all I need to do is open the locker, move one milk crate of stuff out of the way, hook up the pump, drop it into the jug and give it a few squeezes.  I like that.  I'm sure I will dig down to the batteries again after a few months just to confirm that everything is filling properly, but the system seems simple enough that I don't expect any problems.  I think it will be quite the time saver when watering the batteries and will help me keep them in top shape.

Where's The Juice

The house battery bank has become our major task on this stop.  I had hoped we could partially revive the bank and deal with it once we were further south, but it was not meant to be.  Right now one battery has been removed from the bank (suspect an internal short that may have been the cause of the original issue), and the remaining two don't hold much power.

The old battery bank...and some baking soda to neutralize acid

I've been doing research on batteries and have found that many don't consider most of the marine deep cycle batteries to be very good or capable of deep cycles.  Add in the fact that the identical replacement batteries cost $700 each (and I need 3) and spending that kind of scratch on a less than good solution seemed silly.  Golf cart batteries (group size GC2) are generally considered to be much better at deep cycle use, and two of them fit within the footprint of the group 4D batteries (that is the size that currently make up my house bank). They are generally less expensive and have higher amp-hour (Ah) ratings so this decision was fairly easy.

Then came the great AGM versus wet cell debate.  There are certainly pros and cons to both options.  The big pros for AGM are the lower maintenance requirement, low self discharge rate, and faster charging.  The pros for wet cell are they can tolerate overcharging a bit better, seem to have a bit higher capacity, and are cheaper.  To us, it was a real toss up.  The existing batteries are AGM as are the engine start batteries, so we figured we would likely go that route.

That is, until we tried to get some.  The local Napa store didn't have any in stock, and the ones they could get seemed inferior to many others.  The guy at the local golf cart store tried to locate ones from a variety of different suppliers and only found two options.  One he wouldn't be able to get until mid February and the other was over $300 each. On the other hand, he had just received a pallet of 232 Ah wet cell batteries that cost $105 each. We tried looking online for AGM's as well, but between shipping and the inability or cost to ship the old batteries back (cost of batteries usually includes returning the old ones back for recycling...since all that lead is still worth some money) and the resulting core charge we would have to pay (over $200), it wasn't a feasible option.  So, the decision was pretty much made for us...we would go with the wet cell batteries. Since the race between AGM and wet cell was so close in our minds, we really didn't mind this route.

The new batteries

We bought 6 of the US 2200 XC2. These are 6 volt batteries rated at 232 Ah.  By wiring two of these in series, I end up with a 232 Ah 12 volt "battery".  Wiring 3 sets of these in series would give me 696 Ah.  The old batteries were 198 Ah each, so the battery bank, when it was good, was a total of 594 Ah.  This means the new setup will give me an extra 102 Ah.  Of course, for best life you are only supposed to discharge batteries to 50%, so this gives me an extra 51 Ah of usable power.  Not too bad, particularly when you consider the fact that all the batteries cost less than just one of the West Marine batteries.

Of course, the batteries weren't the only cost related to this change.  I needed 3 new cables to connect the 6 volt batteries in series to make 12 volt battery sets.  I considered ordering some custom cables from GenuineDealz (I've purchased wire from them before and have seen their custom assemblies), but being a bit impatient, I opted to have them made locally.  The Napa Auto Parts in Southport stocks a variety of marine grade stuff and that included the 2/0 marine grade wire and crimp on connectors needed to make the cables. They made me the 3 cables I needed for a little under $40.

Getting the old 4D batteries out of their home in the cockpit locker wasn't as bad as I thought it might be.  Doug, the harbormaster at Deep Point Marina, came and helped me lift them out of the locker and get them off the boat and to the car. We put them in some heavy duty trash bags and took them to the battery store to trade them in for the $35 per battery core charge (the golf cart store was nice enough to understand that a 4D battery was roughly equivalent to two "cores" so we could get the 6 core charges refunded with the 3 4D batteries). After getting the batteries out, we had a little cleanup to do.  We ended up using 3 boxes of baking soda and copious amounts of water to clean up the mess we made trying to revive the old batteries.  This took quite a bit of time, but after a few hours the battery box was reasonably clean and ready for the new batteries...or so I thought.

Before I decided to go this way I spoke with a couple of people who owned Leopard 38's and have done this change, and they reported no fit issues.  When I measured the space (as best I could when the old batteries were still sitting in there) it looked like it was going to be close. So, naturally, the batteries didn't quite fit.  I guess my battery box was just a bit smaller than the boats that came after mine, and the two golf cart batteries, when placed end to end, wouldn't quite fit into the tray built to hold the old 4D batteries.  I ended up having to modify the tray so there was enough room. Height was also a minor issue, and I had to modify the ledge that holds the shelf/lid to the battery compartment in order to get the batteries to fit. Not major reconstruction, but not a slide in replacement either.

Minor technical adjustments to the battery box

Finally, after many hours of cleaning and reworking the battery box, the new batteries were placed in the compartment and wired up.  Connections were checked, and after verifying everything looked OK, we flipped the switch and brought the electrical system on the boat back to life.  Before letting the inverter/charger go to work charging the bank, I changed the settings to represent the new battery bank configuration.  Then the charger was started.  It seemed happy with the batteries and charged them up after an hour or so (being new, they were mostly charged when we got them). Since it was getting dark and cold, we decided to finish the last parts of the install in the morning.

The new house battery bank wired up

The next morning I started by running a couple tests to confirm everything was working as it should.  I ran the inverter with high load (our smaller cabin AC unit) and checked temperatures of the batteries, battery terminals, and cables with a non-contact thermometer and only saw a couple degrees of difference after letting the unit run for 15 minutes or so.  I then turned the charger back on and took more measurements to verify everything is fine.

Then came the finish work on the battery box itself.  With the cables attached it took up even more room above the batteries, and I decided I needed a little under an inch of extra height for the lid. I added some wood strips to the battery box lid and mount to give it more clearance for the taller batteries and cables. I also repositioned a couple of the wires to allow better access to the battery vent caps.

Modified ledge so everything fits

The one last hurdle was how to strap the batteries down.  The box had 6 straps and I figured I could use one per battery.  But I didn't take into account the wires and the funky battery caps on the battery.  Simply running a strap over them would hold down the caps so you couldn't open them to add water (a necessary maintenance task on flooded cell batteries) and worst case might even break the caps. I thought about just putting wood blocks on the top of the batteries to hold the strap off of the caps, but I was worried that they could slide and that would result in the straps coming loose.

My solution was to create some wood spacing blocks that would slide in between the battery and tabs of the battery tray and run up the side of the battery.  At the top, a second piece of block was added to sit atop the battery so the straps would hold the batteries down.  This solution will hopefully prevent the batteries from moving side to side as well as allow the straps to hold them down without crushing the battery caps or putting a lot of strain on the cables.

Modified battery box lid and battery hold down shims

Of course, constructing these things and then painting them so they might survive a little while in the harsh environment of a boat battery box has taken a lot of extra time.  The temperatures have been OK here in Southport, but still not good paint drying temperatures. I let the shims dry for a good day, and they still feel just a bit sticky to the touch but I'm sick of waiting.  The batteries are strapped in now and everything is finally back in the locker, and the cockpit is looking a bit more like a cockpit and less like a garage. It has taken me about 5 days to do this battery replacement. I'm still hoping for the day I find a project that doesn't take 10 times longer than I think it should on this boat. But now we seem to have a well functioning battery bank.  Only time will tell if going the golf cart battery route will be worth it.

Getting Things Done

Our trip from Hayes, Virginia, to Southport, North Carolina, in addition to trying to escape the cold, was a bit of a shakedown cruise.  That wasn't really the intention, but as Cap'n Ron said "if it is going to happen, it is going to happen out there".  I guess that is true even when "out there" is motoring along the Atlantic Intracoastal Waterway.  So, since we arrived in Southport, we have been back in fix-it mode.

Before much fixing though, we needed to go fetch our car from the Severn Yachting Center.  We also had a crew member that needed to see a doctor.  Our eldest dog has been battling a condition where one of her ears has sores that don't want to heal (it is called ear margin vasculitis), and a specialist we have been seeing is in Richmond, Virginia.  We decided to combine the trip to get our car with an appointment with this veterinarian.  Our plan was to leave the day or so after we arrived, but a winter storm hit southern Virginia (as well as northern VA, MD, DC, and other nearby areas).  So we pushed it off a few days while I investigated my house battery bank  issue.

On Sunday, we started making our way to Richmond.  We went to visit a friend of my wife in Chapel Hill and stayed with them that night.  The next day we continued our trek to Richmond. Unfortunately, as we were driving, we got a call from the vet.  I guess Richmond was having a hard time dealing with the 10 inches or so of snow and still hadn't cleared the streets after a few days.  As a result, the vet was closed and had to cancel the appointment. We continued on to pick up the car and return both to Southport. We arrived at the marina, said our goodbyes to some friends we made there, and headed back to the boat.

Some of the snow we escaped.

After getting back, the next task was to see if I could locate a small coolant leak in the starboard engine.  I pump the coolant sitting in the bilge into a container to throw away and then look over the engine trying to find the leak.  I find one hose that wasn't clamped all that well and fix that.  Didn't see any other signs of a leak so we clean the engine and bilge, top off the coolant, and test run the engines.  While looking over everything, I start seeing a drip.  Not from the engine or the coolant tanks, but coming from the hose that leads to the overflow tank.  No idea why it wasn't dripping when cold, but it didn't start until everything was warm.  So I drain the overflow tank, pull the hose and check for a leak in the tank.  I didn't find anything so I cut about a half inch off the end of the hose and reconnect it all.  Refill and retest, and everything seems fine now.

While I was in the engine room, I also looked over the alternator.  The tachometer was intermittent at times during the trip, so I checked the connections.  I cleaned the connectors and used a little dielectric grease to help prevent further corrosion, then secured the wires better.  During the test the tach seemed to behave better, so hopefully that is also fixed.  I also took a little time to wire brush and paint the engine and generator as they were showing a little wear and chipping to their corrosion-inhibiting layers of paint.

One of the comments I received from my post on the battery house bank suggested that we might be able to recover the batteries if they weren't too damaged.  I debated this for a while and looked online for information and finally decided to give it a try.  Worst case I figured was that we would still have batteries that needed to be replaced, and best case is we might get a little more life from the batteries. If all it cost us was a dollar or two of distilled water, seemed like it would be worth the risk.  I tried popping one of the dust covers off the battery and find that underneath was a plug that leads to the battery cell.  The plug contains the valve and is sealed with an o-ring so all I had to do was unscrew it.  We added a little distilled water to the cells to see if that would help.  Unfortunately, adding a little water only uncovered the fact that the case was apparently cracked somewhere out of view and the water leaked out of one of the cells creating a bit of a mess.  Guess we will need to replace the batteries before we continue our trip. I'm pretty sure we will go with golf cart batteries, but still debating the pros and cons of AGM versus wet cell versions (as well as trying to figure out how we can source them here).

So, that is where we stand.  Some things we think are fixed, more to go.  At least the weather has improved a bit and is warmer than where we were in Virginia.

Master Of All Trades

"Jack of all trades, master of none" is how the phrase goes, I think.  But on a boat, it seems you need to be more than a jack of several trades, at least if you don't have unlimited funds to pay someone to maintain it.  And certainly if you insist on things being done right. From engine repair to fiberglass, it certainly helps to know how things work and how to fix them, even if you have to learn how as you go.

On our trip south we've discovered a few items that we will need to deal with.  One of them is the house battery bank.  It seems that our house bank isn't holding much of a charge anymore. So begins my deeper education in marine batteries and complex charging systems (if I do any upgrades, I want them to be compatible with the eventual addition of solar). Things I wanted to learn about anyway...but learning under the gun of a needed repair is not as fun.

I'm somewhat familiar with variants of lead-acid batteries and multi-stage chargers from my previous stewardship of an airplane.  In the airplane case, the batteries are small due to weight concerns and expensive (because they are a certified airplane part) and yet need power to crank the engine and run electronics for a while if an alternator failure occurs in flight. So, squeaking out as much life from them as possible was always a goal, and 3~5 years was considered a good lifetime for those batteries. But marine is a bit different environment.  Much larger batteries wired into banks.  The need to run things like refrigerators, lights, and equipment without a charging source for days on end (deep cycling) is a bit different than running a few airplane instruments.

I started my investigation with the obvious...take a look at the house battery bank.  I try to take a peek at all the boat systems periodically, but the house bank sits at the bottom of a locker in the cockpit and isn't the easiest to access. Add in the fact they are AGM VRLA batteries (what was once touted as maintenance-free batteries) and they were a bit out of sight - out of mind.  Well, when i dug all the stuff out of the locker and removed the access panels to the batteries, I could tell that the batteries were not in good shape.  Each of the 3 group 4D (20 inch x 9 inch x 10 inch or so) batteries showed minor signs of swelling.  The two usual causes of this are heat related: Either a sudden rapid discharge (short) or overcharging of the batteries.  Since I haven't experienced any shorts, my immediate assumption was that it was the result of overcharging.

The West Marine Battery that makes up our current house bank.

A year or so ago I had one alternator's voltage regulator fail and it was overcharging...but that problem was identified rather quickly and resolved.  Since the boat is configured so the engines charge their start batteries and then any leftover energy is used to charge the house bank, I would expect the start battery to have failed first. Since it was OK, I doubt it was the culprit.  The original charging system for the boat works in a similar manner, charging the start batteries and then letting power "overflow" from there to charge the house bank.  That left only one culprit - the Xantrex inverter/charger.

The inverter is wired to the main house bank, and it includes a smarter multi-stage charger that is supposed to do a better job of charging and maintaining batteries.  As a result, the charger needs to be set up with parameters for the type and size of the battery bank.  I guess I shouldn't have trusted how the thing had been set up when we bought the boat.  I found the parameters were set for a 3000Ah bank of wet cell batteries.  Since the actual bank is only 600Ah of AGM batteries, this is probably the cause.

Of course, this means we need to replace the main house bank. The batteries currently on the boat are from West Marine and when I checked were about $700 each.  Ouch.  Looking around, I found similar 4D AGM batteries for a little over $400 each.  Continuing my research, I found that many of these batteries aren't true deep cycle batteries and, as a result, likely won't last as long as other options. Reading a number of articles on marine batteries and deep cycling batteries, it seems that some of the best bang for the buck are golf cart batteries.  It sounds like they are better designed for deep discharges than the big batteries.  They also seem to have higher amp-hour ratings for a given size than the ones I have now.  The down side is that each battery is smaller and is only 6 volts, so I would need two batteries connected in series to equal one of the batteries I have now.

Trojan T-105 225Ah, 6v battery option.

US Battery 2200 232Ah, 6v battery option.

Two group size GC2 batteries sitting next to one another are the same length, slightly taller, and just a bit narrower in width than a 4D group size so they should fit my battery locker.  Wired in series, I would have a 12 volt equivalent with between 210 and 225 Ah (compared to the existing batteries at 198Ah). The wet cell batteries seem to be around $110 each (or $220 for the equivalent to one of the 4d's), and the AGM versions are around $200 each (about the same as the cheaper 4D's that I've found). Since these produce a slightly higher amp-hour bank that is more accepting of deeper discharges (to 50%), this may be the way to go.  It would require I get 3 new cables to wire two 6-volt batteries in series, but it seems to me the advantages may be worth the limitations.

Trojan AGM 217Ah, 6v battery.

US Battery AGM 213Ah, 6v battery.

The other question is do we go with AGM or traditional wet cell batteries.  Due to cost, I'm not interested in going with the newer lithium options (my time in the software industry has taught me the value of "trailing edge technology") and these two seem like the best choices.  Each has advantages and disadvantages.  I guess one thing that worries me about the standard flooded battery bank is if we can keep on top of maintenance.  I know they need to be checked and filled with water periodically.  With the location of the house bank being at the bottom of one of our large storage lockers, will we dig everything out and check them as often as we should?  And what is that interval anyway?  But my wallet sure likes the price point of the flooded ones, and they do have higher capacity.

Decisions, decisions...if anyone has any advice, leave a comment.