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Bigger battery bank

April 15, 2022 by Marcy

We are enjoying the new, larger lithium battery bank in our travel trailer.  Boondocking is even easier that it used to be.  Of course, “new” is a relative term, when the date of install was April 24, 2021.  John found an excellent deal on a set of used power supply batteries and it didn’t take much convincing (that I remember) for me to agree that an upgrade would be useful.

Our older lithium battery bank was spec’d at 6.6 kWh and tested at ~6.3 kWh
The new batteries (also lithium) calculate to 11.2 kWh and test at ~10.5 kWh

So a nice 66% increase in capacity, which gives us more flexibility.

The previous set, living on a stand next to the fridge:

Previous battery bank

And a zoomed out view, because I love that we can stick magnets to the refrigerator now:

Previous batteries and fridge

We donated our previous set to an orienteering timing company.  They use a lot of remote power for their equipment, and our batteries are a welcome addition to that setup.  That’s a win in the repurposing column.

We still do not have a battery management system (BMS) on this battery bank.  The batteries had them originally but they no longer worked so John disconnected that part.  This means, among other minor things, that we still need to be careful not to charge them when the temperature around the batteries is below freezing.  Most of the time this isn’t an issue.  The batteries live inside the travel trailer and our preference is that our living quarters are way warmer than that.

The new batteries, unpacked and ready to be installed:

New battery stack

John built a couple racks to hold 5 batteries each:

Battery box

He cleared out the area on either side of the fridge and added a nice floor covering:

New space for batteries

Half of the batteries, fitting nicely in a small closet and enclosed with the rack (now painted white):

Half the new batteries The other half

When we leave for extended periods of time, especially when we store Howie, we have to consider the upcoming overnight low temperatures and whether to leave the solar panels connected to the batteries to keep them charged.  The only appliance that draws power is the refrigerator, and it requires very little.  We can turn off solar charging for over two weeks and still have plenty of battery capacity to keep the fridge powered.  If we ever plan to be gone longer than that in the winter, we would have to consider emptying and turning off the fridge.  That is a rare occurrence, but it is the one time we would miss a BMS.

As an aside, after all our travails with the old fridge (previous post), I have gotten used to having one that just works.  It makes kitchen life easy, and is especially helpful for the longevity of the condiments.

Back to the new (to us) battery bank.  John found a set of ten batteries that cost $130 per kWh, a fantastic deal.  It helps that we aren’t as concerned about a working BMS.  He continues to monitor the cost of batteries, and he tells me that it continues to drop.  The best price he found recently is $300 per kWh for new lithium batteries, including a BMS.  Lithium batteries are getting much more affordable, great news if you live on the road or off-grid, if you’re looking for backup power, or if you have a time-of-use rate schedule (variable prices for electricity depending on time of day).

These ten batteries are 24 volts instead of the 12-volt version we had previously.  John wired them up in parallel, an improvement over the prior “parallel plus series” setup.  We no longer have to concern ourselves with potentially unstable behavior on the low end of the battery charge.

For reference, here is our electricity flow chart:

ACDC diagram

The usable range of these batteries is between ~10% and 100% of maximum, for a total of 90% or 9.5 kWh.  This makes it easy to go boondocking and hardly ever think about running out of electricity.

Especially in the summer when there are many hours of sunshine.  Spring and fall are not a challenge either, if we park Howie with a good view of the sky.  Multiple days of clouds leads to energy conservation, but it’s not nearly as challenging as it was with the smaller battery bank.

In winter we typically hunker down at an RV park and plug in whenever needed.  The heat pump mini split is about as efficient as you can get for heating, still it’s nice to add a ceramic floor-level heater (which uses more power) to help combat the lack of good insulation in our home.  It would take a mild climate and full sun on the roof to allow for full-time boondocking during the shortest days of the year, something we haven’t yet tested for feasibility.

The other half of the battery bank, on the right side of the fridge:

The other half

How long could we go without any incoming solar?  Even a cloudy day yields some amount of charging, although parking under a bunch of trees leans toward worst case.  Here are some examples:

1. Ideal temperatures and with the inverter off, so we are only using the fridge, lights, and other DC items.  I estimate around 0.5 kWh/day for the refrigerator and maybe 0.8 kWh/day for the rest, for a rough estimate of 1.3 kWh/day.  We could run like this for ~7.9 days, i.e. slightly over a week with zero solar to resupply the batteries.

And it would take very little incoming solar to keep us going like this indefinitely.

2. Turning the inverter on and adding electronics like the laptop, a bit of cooking, and the water heater for showers = perhaps around 3.5 kWh/day, which we could do for 2.7 days just on battery power.  Or longer if we were consciously in “conservation mode”

3. Hot temperatures so we are running AC during the day = maybe 5.5 kWh per day, or 1.7 days without incoming solar.  In this situation we would probably be resigned to sweating more.  Thankfully, it is rare that we are somewhere this hot without sun overhead, and the heat pump air conditioner is quite efficient.  Most of the time when it’s hot, sun is powering the air conditioner and charging the batteries at the same time, so we’re plenty comfortable boondocking in the summer.

4. Cold temperatures, especially in the winter, are the biggest challenge.  If the heaters are working to keep us from freezing, we can use 7.5-9.5 kWh per day (or more), so about 1 day’s worth of battery capacity.  If we are relying on incoming solar to make this happen, we would probably set the heat pump temperature low, bundle up in a lot of clothes, use sleeping bags at night, leave the ceramic heater off, etc. in order to conserve the battery.

Much more typically, in cases #1-3 we have more than enough sunshine to keep us going indefinitely.  We usually don’t plug in at all in the summertime.  And as I mentioned for case #4, we typically live in an RV park (plugged in at least part of the time) during the coldest/darkest parts of the winter.

Examples of incoming solar, with 1580 watts worth of solar panels on our roof:
Under trees with some sun in the spring/fall = 2-4 kWh/day
In winter with full sun = 3-5 kWh/day
Spring/fall with full sun = 5-7 kWh/day
Full sun in the summer = up to 10 kWh/day

Bottom line, this lithium battery bank is working great in our travel trailer.  I’m grateful John found these batteries and was able to set them up in Howie.  Our all-electric home has the perfect system for us, now we just need an electric truck to tow it!

Category iconAction Tag iconBatteries,  Camping,  Electricity,  Howie,  Travel trailer

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