What is a good way to test a LiFePo4 battery if you only have basic equipment?

[Calvin98]

I just got a Chins 100Ah battery at Walmart. Have 90 days return window. How to test it to make sure it is good and reliable? Have a Renogy current shunt, volt meter, clamp on amp meter, 10A LI battery charger but that is about it. Oh, have a 100A Harbor Freight battery tester. I use the LI charger to charge the battery to 100%. Used a camper fridge pulling 10.3A load to run the battery down to a few percent in a little over 9.5 hrs. So capacity is ok at about 97ah before I stopped it. Now doing 80% to 20% tests. Run the fridge from 80% to 20%, then use the 10A charger to charge back to 80%. Repeat a few times.
How long to do this? Days ?Weeks?
Better tests to do?
If it is good now, nothing to worry about?
Heavier load tests? 50A draw? 100A draw? Don't have anything that will pull those kinds of loads. I have a lead acid Harbor Freight 100A heating element type tester that can do big loads, but you have to keep your finger on the switch and you can't leave it on for very long. Minutes ok, hrs, no.
Run battery down to where the BMS shuts it off? and repeat a few times?
If theses batteries fail, do they fail right away or months/weeks later? (if at all)?
Just have 90 days and did not want to buy 100's of dollars worth of test equipment to say that a $250 battery is ok.

 

[timselectric]

It seems ok.

 

[timselectric]

Standard capacity test is 20% discharge from 3.65v per cell to 2.5v lowest cell.

 

[webbbn]

You bought it at Walmart. What could go wrong? (kidding)

I agree with @timselectric, I think you've tested it enough. If you can cycle it and get the expected energy in/out, and if it can put out 100A for any length of time without issue, there's not much more to test.

 

[RV10flyer]

Run it on all your normal loads for 89 days. If it does good, you got a keeper. I wasted money on test equipment for grade b junk, then I found good quality cells from Amy at SLT and then 18650 Battery. Never tested another from 28kWh to 200+. Lovin the OG life 19+mo.

 

[Calvin98]

You bought it at Walmart. What could go wrong? (kidding)

I agree with @timselectric, I think you've tested it enough. If you can cycle it and get the expected energy in/out, and if it can put out 100A for any length of time without issue, there's not much more to test.

I have not done a 100A test with the load tester yet. I just have it. Ok, for how long? 1 minute? Few minutes? Other?
It is a closed battery and no Bluetooth, so no idea what individual cell voltages are.

 

[Calvin98]

Run it on all your normal loads for 89 days. If it does good, you got a keeper. I wasted money on test equipment for grade b junk, then I found good quality cells from Amy at SLT and then 18650 Battery. Never tested another from 28kWh to 200+. Lovin the OG life 19+mo.

I just did not want to deal with No Return policy on Amazon and have to plead with Chins that the battery was bad if it was bad. At Walmart, I at least have 90 days to figure it out and can return to store.

 

[webbbn]

I have not done a 100A test with the load tester yet. I just have it. Ok, for how long? 1 minute? Few minutes? Other?
It is a closed battery and no Bluetooth, so no idea what individual cell voltages are.

If it can put out 100A without significant voltage drop for a minute, it should be able to put that out indefinitely (until it's drained, of course). The current capacity is determined by the internal resistance, which shouldn't change significantly until the battery starts failing.

You can't be 100% sure that it's not going to fail tomorrow (or, more likely, at day 91), but if it can cycle to close to what it's rated at and sustain the maximum current that you need for any length of time, there's not much else you can test without much more equipment.

 

[boenjames]

Standard capacity test is 20% discharge from 3.65v per cell to 2.5v lowest cell.

Hi Tim and all,

So i have 15S 48V 100Ah x 2 units, i currently set cut off to 47v, should i change to 37.5v (2.5v x 15) per battery instead?

 

[Calvin98]

Thanks! Will try 100A load and report. The load tester still cost only $20 at HF.

 

[timselectric]

Hi Tim and all,

So i have 15S 48V 100Ah x 2 units, i currently set cut off to 47v, should i change to 37.5v (2.5v x 15) per battery instead?

The BMS should shut down when the first cell hit 2.5v.
The inverter should shut down before that.
The BMS shut down should be a last resort.

 

[Calvin98]

Did a 100A load test for 20sec and it passed. Could not do any longer cause the heating element was smoking the paint on the case.