The House Battery Project

We enjoy staying off-grid (boondocking), but we found over the past year or so that our house batteries were not performing up to their capacity, and we would need to run the generator to get the batteries up to charge even if we were getting solar energy from the solar panels. We had 8 6V golf cart deep cycle flooded lead acid batteries that required maintenance of checking the water levels and adding distilled water if they got low. They needed to be in a compartment that has access to fresh air as they off-gas during their charging and discharging. Characteristics of flooded lead acid batteries are that they have a limited number of charge/discharge deep cycles (we've seen indication of 200-500) and that they should not be discharged below 50% of their power or their lifecycle will be shortened. The 8 6V batteries that we had were rated at 840Ah (amp-hours) of 12V power, of which we had 420Ah usable (50%). To give you an idea of what this means in our "house", when we view the information provided by the inverter, the normal draws on our system are 25-30A (residential refrigerator, inverter, lights, phantom loads from laptops, TVs, etc). So, in one hour, we use 25-30Ah. If we are drawing 25A for 10 hours, that's 250Ah. For all day, that's 600Ah (25A*24hours). The 420Ah would not provide enough power for all day unless additional power was being provided from the solar panels or generator (or being plugged in to shore power). Each of the days that we used the batteries had a possibility of producing a "-1" to the available charge/discharge count (depending on how deeply we discharged the batteries). We would turn off our residential refrigerator at night (since we weren't opening the door, it wasn't a problem with things warming up inside the refrigerator or freezer) to cause less draw on the batteries. In short, our batteries were at the edge of being functional for our needs, and were not giving us the rated power because they were near end of life.

Carl had been doing research, and we had discussed different options. Three and a half years ago, Dwayne and I had put AGMs into Miss Doozie (https://trekincartwrights.blogspot.com/2018/03/sunday-and-monday-solar-progress.html) -- at that time, we had decided that lithium batteries were too new a technology, too costly, and the location where our house batteries would be installed on the Bluebird (engine compartment) was too dirty to make Lithium an option (we knew of folks who installed their Lithium batteries inside their motorhome, taking one of the clothing drawers (*precious* drawer space!) for the batteries -- I was *not* interested in doing that!). AGM is a better choice than flooded lead acid (no maintenance, more charge/discharge cycles); they are still lead acid batteries, sometimes known as sealed lead acid. 

Carl and I felt that lithium batteries (more exactly, Lithium Ion Phosphate (LiFePO4)) have matured significantly in the past few years, and we have seen lots of people using them with solar applications in RVs. The prices have come down, the bay where the batteries are located on Gracie is relatively clean, so we decided that it was appropriate for us to go with lithium at this point.

(Some information comparing flooded, sealed lead acid, and lithium batteries can be found here: https://unboundsolar.com/blog/lead-acid-vs-lithium-batteries)

Carl had researched lithium batteries from many sources, and we decided to go with Ampere Time 12V 300Ah lithium batteries from Amazon (https://smile.amazon.com/dp/B08K7HZ6KZ?ref=ppx_yo2_dt_b_product_details&th=1). Unlike lead acid batteries, lithium are supposed to be able to be fully discharged without negative consequences to the batteries (we have seen recommendations to limit discharge to 5%). Based on what I wrote above, that we had usable 420Ah with our golf cart batteries, theoretically, two of these lithium batteries would give us almost 50% more power. But... we went with 3(!) of these batteries, for 900Ah. With these batteries, we should be able to go multiple days using solar power alone, even accounting for cloudy days when we don't get a lot of charging from the sun. We should also be able to run some additional electric appliances - the Keurig to make Carl's coffee in the morning, microwave to do heating up for lunch or supper, heating pad for relief of aches and pains, leaving the refrigerator running day and night, etc.. These batteries are rated for 4000+ deep cycles (compared to 200-500 for the golf cart batteries). The 3 12V 300Ah batteries fit into about the same footprint as the 8 golf cart batteries, and they weigh about 270 pounds less (Gracie will get better fuel mileage, right? uhm, maybe not that large of a weight change overall!). There is not a requirement that they be in an open compartment. The only concerns with lithium batteries is that they should not be charged if the temperature is below freezing (0C, 32F) and should not be discharged if the temperature is below -20C (-4F). In general, we are not in freezing temperatures, but there are some days and nights that it may dip below freezing. If we are boondocking, the solar controller is programmed to *not* send charge to the batteries under 35F (to give us a buffer) -- the temperature is monitored via a probe on the batteries. If we run the generator when it is under 32F, we will need to make sure that the charger from the inverter is turned off, and the same if we are plugged in to shore power. (So far in our monitoring, even though the outside temperature has supposedly gotten down to 30-31F, the temperature monitor on the batteries is indicating 46F, so it appears that the bay is staying warmer than outside.)

We had ordered the batteries when we were in Delaware and had them shipped to my cousin's home in Delaware (since there is no sales tax charged in Delaware -- you know RVers, they are always looking for a deal!). We had carried them with us in the Jeep and they had been sitting in Jimmy's shop for a few weeks. Last Saturday, after Gracie's maintenance in the shop was completed, and while Jimmy was changing out the engine batteries, Carl started the task of replacing the house batteries as well.

Starting to disconnect the 8 6V batteries. Note that while Carl was working on this project, we could have no power to the coach.

Checking the weight on the 6V batteries - a single one was 59.8 pounds -- about 480 pounds for all 8 of them.

The batteries were on a tray since the water in them needed to be checked -- Carl had a watering system on the back 4 batteries (the least accessible) so he could add water without having to get all the way to the back of the bay.

We took the tray all the way out to be able to clean the area. After getting the rolling tray out, since the lithium batteries will not require maintenance, we decided to remove it completely from the compartment to give more usable space.

After taking the tray out and cleaning the metal underneath, Carl coated the metal with transmission fluid to prevent oxidation / rust.

We put a piece of plywood down to provide some strengthening and insulation, and then started putting the lithium batteries in.

Carl and Jimmy putting the last of the three lithium batteries into the compartment - each weighs about 70 pounds, so 210 pounds total (compared to 480 for the golf cart batteries).

We decided to keep the packing material (a dense Styrofoam) on the bottoms of the batteries, also to provide some insulation.

Initially, Carl hooked up only one of the batteries, sufficient for us to be able to plug into shore power for the coach since it was getting late and he didn't want to rush getting all of the connections completed.

The next afternoon, Carl and Jimmy were working on securing the batteries with a strap so they won't move around.

Wiring completed for all three batteries on Wednesday afternoon. There is plenty of room beside and in front of the batteries in the compartment to store the various liquids that we carry along (antifreeze (one for Jeep, another for Gracie), Oasis transfer fluid, windshield washer fluid, oil).

While examining the space for the batteries, Carl pointed out to Jimmy the large space beyond this compartment in the middle of the coach, behind the fuel tank. They have discussed (a future project?) making a space in there and moving the batteries into it, giving us this whole compartment for additional storage. Jimmy said that when he said that, both Carl's and my eyes lit up like he had shown us buried treasure -- which is appropriate -- storage in the motorhome is precious!