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Buyer beware big battery A123s

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Sep 27, 2020
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Was very excited to receive 2 of the advertised 24V plug and play A123 battery boxes from bigbattery. That excitement faded fast during the first charge. I am replacing a 48 V leadacid system and set the new batteries in series settind the fm80 well within the published battery specs. Nearing absorb voltage the battery voltages started to diverge drastically by about 0.7V so I stopped the charge test while on batt was still well below absorb. I have since done a discharge test and it looks worse than anything else I have heard thus far. On cell is waaayyyyy low on charge and discharge and several others are alightly out of balance.
Then did some forum searching and found other instances of mis balanced and possible bad cells. Definitely wish i would have read those before ordering. Now it looks like I'm stuck with a bad battery.
I will follow up with the test results later. I jist wanted to get word out that these batteries are fairly cheap for a reason. All made the more complicated by the $275 freight to Hawaii. Feeling pretty screwed...
 
If the SAME cell is both low on charge and discharge, it's likely just imbalanced. If it was HIGH on charge and LOW on discharge, it's a weak/defective cell.

Most of the results I have seen are simply minor to moderate imbalance issues.

If you don't have a programmable BMS, your best bet is to find the absorption voltage that doesn't set the BMS off and continually charge to that level. As you cycle it, it should improve. Shallow discharges to 3.3V/cell will help expedite top balancing.

How did your discharge test compare to rated?
 
Agree with snoobler. Two cells on one of my two A123 24V batteries were both low on charge and discharge. I finally made them balanced by using the static balance feature offered by Overkill/JBD BMS (Xiaoxiang App).

By the way, contacting the BigBattery didn't help at all. I dropped them an email to ask questions about the weak(unbalanced) cells and low capacity (due to the unbalanced cells) of A123 24V battery on Aug. 31st, and haven't receive any response yet. My gut tells me that either they are super super busy or they have strong confidence on what they sold and don't believe what I said. Anyway I solved the problem and would think twice when considering buying stuff from BB next time.
 
Well after two weeks of charge and discharge cycles, It looks like the BMS failed on one of the batteries and bricked one of the cells or maybe the other way around.
 
Voltage of one cell at 0.0 and wont budge attempting to recharge. The BMS does succeed in generating a surprising amount of heat though. Stopping tests and hoping big battery has a solution cause I am one unhappy camper. Avoid these guys like the plague!
 
I purchased 3 of these and have only tested 1, but all three have charged to 28.8 and held 28.6 after resting. I am new at this so take it with a grain of salt.
 
I purchased 3 of these and have only tested 1, but all three have charged to 28.8 and held 28.6 after resting. I am new at this so take it with a grain of salt.
Thank you for sharing. If you can hit 28.8v with ease then dropping them to 20v should be no problem. Obviously this should only be done once to test capacity, as going from 0 to 100% everyday would be a quick way to kill the batteries. I know you got the plug and plug version but that should make no difference. I'm wondering what charger your using, maybe it has a profile suited for these Nanophosphate cells
 
Thank you for sharing. If you can hit 28.8v with ease then dropping them to 20v should be no problem. Obviously this should only be done once to test capacity, as going from 0 to 100% everyday would be a quick way to kill the batteries. I know you got the plug and plug version but that should make no difference. I'm wondering what charger your using, maybe it has a profile suited for these Nanophosphate cells
I’m using the LV2424 hooked up to utility to charge, using the custom profile settings Will recommended.
 
@johnnyding I’m having the same problem as @apocalypseINparadise . Can you confirm you were able to hit 20v-28.8v? I have cells hitting the upper and lower limit no matter what balancing settings I configure
I only let my battery pack hit 20-28.8v when doing the capacity test. I set my BMS to 24-27.2 (3-3.4V per cell) for daily use. The BB's BMS is different to what I am using (overkill BMS), so I have no idea why your battery pack always hit the 20-28.8 range.
 
I only let my battery pack hit 20-28.8v when doing the capacity test. I set my BMS to 24-27.2 (3-3.4V per cell) for daily use. The BB's BMS is different to what I am using (overkill BMS), so I have no idea why your battery pack always hit the 20-28.8 range.
I have the overkill BMS as well, I was attempting a a capacity test but can barley hit 28v without certain cells hitting their limit. I wouldn't cycle 20-28.8v normally. Thanks for confirming you were able to reach 28.8v
 
I have the overkill BMS as well, I was attempting a a capacity test but can barley hit 28v without certain cells hitting their limit. I wouldn't cycle 20-28.8v normally. Thanks for confirming you were able to reach 28.8v
This does not reconcile with the things your said in the top balance thread.
 
Sorry to expose my ignorance here, but with my BB plug & play 24v unit and MPP Solar LV2424-MSD I don't see individual cell performance or voltages. Perhaps I need to hook up the USB communication cable to a computer and run the Watchtower ("Powerwatch???) or whichever software in order to see individual cell reports?
 
I purchased 3 of these and have only tested 1, but all three have charged to 28.8 and held 28.6 after resting. I am new at this so take it with a grain of salt.
I too have had good luck with the two I purchased, especially when I set my magnum pt-100 dip switches to the AGM2 setting. In my case this provides a 29v absorption charge. I did take both my cases apart and was astonished at the poorly routed and undersized main wires as well as the haphazard battery padding placement. They are working well after two years so damn the torpedoes...full speed ahead!
 
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