Do i have a bad cell?

[topperharley]

I have 3 200ah 12v batteries i built about 4 years ago. They've worked great thus far. Currently dry camping so monitoring battery performance and I've noticed my battery 1 is pretty much doing nothing. When discharge is turned off, all 4 cells show 3.3xx. as soon as i turn discharging on, cell #4 drops to 2.7/2.8v. the max discharge, if any at all, doesn't exceed 1a. During charging while running my generator, it doesn't charge more than 1a and cell #4 is being balanced at 3.6/3.7v often triggering a cell over voltage.

I'm going to take it out and try to top balance it when i get home, but it's this cell pretty much done? Would i be wasting my time top balancing? What's the best strategy to replace the cell if no good, find an identical replacement or just replace all 4?

 

[hwy17]

If the cell is reliably the first to high and first to go low then yes it's probably done.

 

[topperharley]

Where do we land on replacing the 1 cell vs all 4?

 

[topperharley]

Also any suggestions on best place to buy? I originally bought these from aliexpress i think. My set up is perfectly designed to fit the 3 batteries i made, so i can't exactly drop a name brand in the place of the non working battery

 

[RCinFLA]

Check terminal connections on bad battery. Check voltage on cell terminal base of suspect cell with multimeter.

BMS cells sense wires are shared between adjacent cells so a poor bus bar connection can show up as low cell voltage on one cell when current is drawn on battery.

 

[SparkyJJO]

Check terminal connections on bad battery. Check voltage on cell terminal base of suspect cell with multimeter.

This.

 

[Skypower]

Check terminal connections on bad battery. Check voltage on cell terminal base of suspect cell with multimeter.

BMS cells sense wires are shared between adjacent cells so a poor bus bar connection can show up as low cell voltage on one cell when current is drawn on battery.

If it’s not this, then I’d be thinking bad cell. Don’t be running any current through it till you check this.

 

[topperharley]

Ok thanks. Yeah I've turned it off for now and will be doing a more thorough checking/testing of it when i get home.

I can't even find 200ah cells, closest i can find is 230ah, so i guess if it's def bad I'm buying 4 new cells.

 

[Skypower]

If I were a betting man, I’d say that it’s a loose buss or terminal lug. Mobile applications are hard on fastener terminals. Vibration loosening. If that’s the case, I just hope it didn’t get too hot. Look for discoloration from heat

 

[topperharley]

This is true. I can't remember if i used lock washers or not. I can't open my battery box without completely disconnecting the system so i can't check until Monday at the earliest. Hopefully it's just a loose connection. Bms shows only 26 full cycles. I'd be pretty disappointed if the cell went bad