LifePO4 battery Shorted?

[tmckenna]

I built a small battery bank for a very specific project, which consisted of 4x 16ah lifepo4 batteries wired in parallel. I've had the bank for a while now but never had the ability to test capacity. I finally got a Renogy battery monitor and during the calibration realized that my batteries only seem to be holding about 2/3s of what they should be. Both discharging and charging calibrations only showed approximately 44ah of capacity, 20ah short of what should be a total of 64ah. Now during my wiring I had a small mishap and contacted the 2 terminals of one battery together. I tested the voltage (individual from the rest of the batteries) and it seems to be correct. Could the battery be trashed but still display 14v? Its the only explanation I could think of for being 20ah short of max capacity?

 

[tmckenna]

The battery in question is a "Miady" from amazon, I know theyre not super high end lifepo4 but i guess i figured the BMS would protect that battery from completely dying in the event of a short.

 

[agt]

I’m also running 4 of those Miady 16AH in parallel. Their BMS does protect (shutdown) against a dead short - I wouldn’t worry about damage from a single incident.

As for capacity - I’ve gotten 750wh out of my packs, discharging at 0.1C (75W lamp) down to my inverters’ low battery shutdown @10.9V, which amounts to 90% of the advertised capacity.

What watt/amp load are you using for your capacity testing?

 

[Substrate]

Um, have you merely wired them in parallel, and using them in a "ladder connect" environment, where you are only connecting your power to one of the batteries on the end?

Or, in this case, are you using a diagonal arrangement, where you take the positive from one battery at the end of the bank, and the negative from the battery on the other end?

If you are in a ladder-type arrangement, that's not the best idea as the one to which the terminal are attached usually gets worked harder.

I'd be tempted to disconnect the bank, charge each battery up individually (and optionally perform a capacity test on each one to see if damage / wear is considerable). Then reconnect it all after fully charging each, and make sure you use the diagonal connection of positive and negative on opposite ends of bank when you run the in parallel like this.

Just my 2c..