Ramblings of a Techno-Viking

The Best Battery for Full-Time Boondocking: LiFePO4

For use as a house battery for a full-time boondocker, prismatic Lithium Ferric Phosphate batteries have huge advantages over Lead-Acid (including AGM and Gel). Half as many amp-hours have more usable power, you don't need as much solar to charge them, and generator run-time for when that is needed is reduced by a lot. Lifetime is much longer as well, but how much is difficult to know since there have not been long-term studies at "low" charge and discharge rates yet and no one has had them long enough to wear them out without mistreating them. (For use as a house battery, seven to ten years is a reasonable expectation.)

While not everyone will agree, I do not believe a BMS is needed for this usage. Anyone that can handle a Lead-Acid bank should have no trouble avoiding over-discharge, and charging at 1/2 C or less tends to put the cells into balance. (For multiple C charge or discharge, a BMS may be a good idea.)

Rarely mentioned is that you can get by with less solar when using LiFePO4. Besides them being more efficient batteries, they do not need the slow finishing charge of Lead-Acid, and they prefer not to be fully charged rather than having their life reduced by not being fully charged. While it will vary depending on your usage, you can probably have a happy battery bank with 25-50% less solar than would be needed for Lead-Acid.

Unless the battery temperature is near or below freezing, LiFePO4 can be charged from "empty" (10-20% of rated capacity) to full rather fast. 1/2 C for my 260 Amp-Hour pack is 130 Amps, which neither my solar or converter-charger can supply. Combined with not needing to get the pack to full, this means much less generator run time is needed when the solar is not able to keep up.

LiFePO4 is not the same as other lithium batteries, and should not be lumped with them. They perform better (but differently) at fractional-C applications than at high-current ones like electric vehicles, so the recommendations for that use should not be used as a guide how to treat them for house batteries.

What is critical for a long-life LiFePO4 house bank setup is properly set charging equipment. They are not drop-in for Lead-Acid, and will be prematurely killed by treating them as one. For solar charging, I recommend 14.0 volts maximum with 1/2 hour hold time and 13.4 volt float. This will charge them near full then not discharge much during remaining daylight. For a converter-charger I would use 14.2 volts maximum (higher voltage because of the higher current) and 13.2 volts as the float, since LiFePO4 does not like being left for long periods fully charged. With my current converter-charger, I just turn it off after the battery is fully charged.

The lifepo4-resources page I have is updated as I find new information. After a year of use, they are out-performing what I had hoped for them.

Do you charge at all from the alternator on the engine? If so do you have a modified alternator and/or regulator?

Thanks, George

Comment by George Monday 02 February 2015 15:21 UTC
As I have mentioned before, I left the alternator charging alone and do not consider it a significant source of charging of my LiFePO4 bank.
Comment by blarson Tuesday 03 February 2015 20:45 UTC
another year has passed. Update please. In southern CA, who would you purchase from again? Thanks
Comment by bob swanson Tuesday 22 December 2015 16:13 UTC