A Simple Question About LiFePO4 Batteries

On Tuesday, May 15, 2018 at 11:59:54 PM UTC-4, wrote:
I have a friend that built several, 4 two for him and two for me 13.2 volt 11AH lifepo4 that used round cells and a bms circuit. for about $50 each that was the same size as the standard 12volt 7ah agm. They went with my Ventus but was a great system. Now I have to talk him into building a few more for my 27 although the 27 came with two lifepo4's one K2 and one bienno both look a few years old and have great capacity so far.

CH

The first "actual" answer to the specific question - and it only took 20 some-odd messages to get it :-)

I took apart a commercially built "drop in replacement" LiFePo4 battery a couple of years ago, and my sense was that there was a bit of wasted space. I suspect the idea was to provide a capacity and footprint that was identical to the SLA batteries they replaced. I did the same googling when I was in the market, and I didn't find anything with significantly more than 10ah stated capacity in the same footprint.

FWIW, I run a load test of my LiFePo4s at the beginning of every season. My K2s currently show about 9.4-9.5 Ah at 0.1c discharge rate. What is remarkable is how flat the voltage drop is in comparison to the old SLA/AGM batteries. (Dick's post above shows a graph).

My K2s are both 4 years old. I did have one go south, but it was stored fully/deeply discharged after a long end-of season ridge mission. K2 gave me a partial credit for a replacement even though it was stored against their recommendations.

FWIW

P3