Load hardware to test capacity.

[Baughb]

3 year old 100ah 12v lifepo4 battery from reputable contributor to this and other sites.
Well cared for and stored and used according to proper practices.
After it was stored for a Nevada winter inside the house, the BMS says that it is 100% at 70ah, not 100ah.
Manufacturer said to find a controllable load to test if the battery actually goes dead after 70ah or 100ah.

I want to put a constant, controlled, consistent measurable load of 1a to 5a 12v on that battery and see how long it lasts.
None of my electric 12v loads are consistent enough to be even close to precise.

Any suggestions and model numbers appreciated.

Bob

 

[Hedges]

I connected my AGM batteries to an inverter and plugged in an electric radiator. Also a mechanical timer.
I measured power draw and saw from timer how long it ran to disconnect (inverter determining 30% SoC)
Include inverter efficiency somehow - maybe measure DC voltage and current once to determine efficiency, then assume AC load is constant watts.

Your battery may need a cycle to reset BMS readings.

 

[Baughb]

I connected my AGM batteries to an inverter and plugged in an electric radiator. Also a mechanical timer.
I measured power draw and saw from timer how long it ran to disconnect (inverter determining 30% SoC)
Include inverter efficiency somehow - maybe measure DC voltage and current once to determine efficiency, then assume AC load is constant watts.

Your battery may need a cycle to reset BMS readings.

Thank you for the suggestions. I have been meaning to get an inverter as I stay 12v in my little systems. That may be a lot faster.
Battery has been cycled at least 3 times since the discrepancy appeared.

 

[efficientPV]

Depends on what you have around. I have a cheap battery tester that is only 1A, Who wants to wait around for that even at 70AH. You could add a relay to that and another resistor to that and boost it up to 5A. I have digital voltage relays that only cost $2 to stop the drain at desired voltage. Add any $10 power meter and you are set. To start with nothing is an investment.

 

[chrisski]

to test sells cells, i use something like the varstay 180 watt battery capacity tester on Amazon. I can't post a link now, but will provide fairly accurate data on how long it takes to drain a battery to a certain voltage and how many amp hours were used.

it is a bit more expensive on Amazon than on Alibaba, but Amazon will ship much quicker. 1/3 the price on Alibaba.