Damaged batteries? 3,2v to 1-2v

[hackenstein]

Hi all,
I went to my cottage to bring my batteries back home to rebalance them. It is winter here. I know they should not be stored for too long in cold. They had 3v when I checked in december. Now they have between 1 to 2,3v. Are they completely destroyed? It is total 8 batteries.

 

[Bluedog225]

Good morning.

What is the battery chemistry?

And I’d warm them completely for a day before doing anything (charging). To make sure the core is warmed.

 

[hackenstein]

Good morning.

What is the battery chemistry?

And I’d warm them completely for a day before doing anything (charging). To make sure the core is warmed.

Lifepo4, okay I have them in warm now.

 

[hackenstein]

Maybe it was the BMS that discharged the batteries? It is the same model as Overkill. Nothing else was connected.

God damn it this was not good.

 

[Bluedog225]

Others who know more will chime in. But as far as I know, no problem. They are fine.

The only dangers are charging cold. And storing hot.

I’d wait for the experts to chime in though.

 

[hackenstein]

The one at 1v has increased now to 1,4. Must be the warmth?

 

[RCinFLA]

One month at 1 to 2 volts is likely not enough time to grow significant dendrites.

Just charge it with lower current until cell gets above 3v. Reason for low initial charge current is if there is shorts it will prevent too much cell heating that can cause thermal runaway.

 

[hackenstein]

One month at 1 to 2 volts is likely not enough time to grow significant dendrites.

Just charge it with lower current until cell gets above 3v. Reason for low initial charge current is if there is shorts it will prevent too much cell heating that can cause thermal runaway.

Okay, is there any way I can check if they got damaged? I have a capacity tester and a volt meter.

 

[hackenstein]

And is it possible it can go from 3v to 1 only by cold in three months? It can go from 0c to -20c here. Or can it be the BMS that caused it?

 

[RCinFLA]

And is it possible it can go from 3v to 1 only by cold in three months? It can go from 0c to -20c here. Or can it be the BMS that caused it?

Isn't much capacity left at 3.0v. Just a little current drain will eat up the 1-2% capacity left below 3v.

Low temp reduces cell self leakage rate.

 

[hackenstein]

Isn't much capacity left at 3.0v. Just a little current drain will eat up the 1-2% capacity left below 3v.

Low temp reduces cell self leakage rate.

Is there a way I can see if any cells are damaged? These are 8p 280AH cells. I have 8 more cells and Im afraid of making it a 16s if there is some that are damaged. Is it enough to do a capacity test? Or should I check internal resistance?

 

[RCinFLA]

Even if not damaged, they are likely 'aged' more than unused cells. They will not likely be matched.

The more mismatched the series connected cells are, the tougher it will be to keep them balanced in SoC.

You can check for cell matching by measuring cell voltage slump from rested no load terminal voltage with a moderate load current for 3 minutes. Make the cell terminal voltage measurement directly on cell terminal base. Matched cells have similar voltage slump for given load current. As cells age their voltage slump for given load current increases.

The load test should be done between 40% and 80% state of charge and 20-27 degs C ambient temperature. Allow 5 minutes of rest, no-load time before taking open circuit no load cell voltage. Make loaded cell voltage measurement at about 3 minutes into load current.

 

[hackenstein]

Even if not damaged, they are likely 'aged' more than unused cells. They will not likely be matched.

The more mismatched the series connected cells are, the tougher it will be to keep them balanced in SoC.

You can check for cell matching by measuring cell voltage slump from rested no load terminal voltage with a moderate load current for 3 minutes. Make the cell terminal voltage measurement directly on cell terminal base. Matched cells have similar voltage slump for given load current. As cells age their voltage slump for given load current increases.

The load test should be done between 40% and 80% state of charge and 20-27 degs C ambient temperature. Allow 5 minutes of rest, no-load time before taking open circuit no load cell voltage. Make loaded cell voltage measurement at about 3 minutes into load current.

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Thanks for the help. It seems to take charge well. Feels like charging for ages I will do the DC load measurement after finnished. Just need to find something to run I only have the capacity tester on 180w it might not be enough?

If these 8 "old 1 year old" cells act pretty normal. Should I skip adding them to the 16s with the 8 new cells. And make two 8s parallel instead? Creating two batteries. As u said it seems to not be a good idea to mix old and new cells in a battery.

And can I do that measurement on these two 8s? Measure what happens whit a big load. I have a inverter for 24v. But I guess its more important to check each cells that got low voltage first.

 

[Rednecktek]

If you're doing a 24v system, go for 2 8s packs. You gain redundancy and reduce the working load on 1 BMS. Since most BMS's are rated for 100a draw, 2 in parallel gives you 4800w max draw vs the 2400w of a 8s2p pack.

 

[GSXR1000]

I would not leave cell stored at 3.0 volts (less then 5%). that is already almost dead. next time you are leaving then for any time set your bms disconnect at 3.2v

 

[hackenstein]

I would recommend that you bring the batteries back to room temperature, and then check their voltage again. If they are still low, you may need to replace them.

The lowest raised to 1,4. And I have charged all now and they seem to keep the charge. I will do the load test and capacity test to each of them.