Discharge issue with SOK 206Ah lithium battery

[RaZar]

I have a 206Ah SOK battery with a MPPSolar 12v all-in-one inverter/charger in a Mercedes Sprinter van that I installed last fall. I used the battery to charge small-draw appliances for short periods without any power source to make sure everything worked (it did). There was a small drop in voltage in the battery. Over winter I disconnected all the appliances, but left the inverter-charger attached to the battery but turned off. Temps this winter occasionally dropped beneath 0 deg F. Last week I found the battery drained to 3.4v. Last night I was able to charge the battery to about 12.8 volts using shore power, at which point the utility stopped charging. Sometime between then and this morning the battery voltage has dropped to 12.0v, and looks to be continuing to drop. No draw from appliances - they were switched off at the master switch. I left the inverter/charger on, and shore power available, and it did kick in for a short period. I don't have my solar connected yet (though its just warm enough to do that now). My question is whether the inverter/ charger, connected to the battery but not turned on, combined with the cold could draw enough from the battery to make it drop to very low. Or.. have I damaged the battery be letting it get too cold, or...is there no problem. And if there is damage to the battery what might it be and how can I tell? If there is damage is there a fix?
Please remember I'm a rookie so simple explanations are really important!

Thanks,
Ken

 

[MisterSandals]

Last week I found the battery drained to 3.4v.

Yow!

No draw from appliances - they were switched off at the master switch.

Is there a BMS? W/bluetooth? These use power.

Last night I was able to charge the battery to about 12.8 volts using shore power, at which point the utility stopped charging.

Why only charge to 10% SoC? Your "utility" charges your battery? What is the "utility"?

 

[rmaddy]

Last week I found the battery drained to 3.4v.

The BMS probably shut down due to low voltage disconnect so when you tried to measure the voltage it appears extremely low.

Last night I was able to charge the battery to about 12.8 volts

That's only about 20% SOC.

Sometime between then and this morning the battery voltage has dropped to 12.0v

That's under 10% SOC.

My question is whether the inverter/ charger, connected to the battery but not turned on, combined with the cold could draw enough from the battery to make it drop to very low.

What inverter/charger do you have? Even off, many inverter chargers will have a very small idle power usage. Left like that for months it's certainly possible, especially if the battery was already pretty low.

You should leave an LiFePO₄ battery (such as the SOK) at about 50% SOC for storage. You should also disconnect everything, not just turned off. Disconnect switches are a good idea if you don't want to physically disconnect one of the battery cables for storage.

I suggest fully charging the battery to 100% SOC and then seeing how it performs. Do you have a shunt that shows you the actual SOC of the battery? If not it would be a good idea to add one to your system.

I don't have my solar connected yet (though its just warm enough to do that now).

Why wasn't your solar connected in the colder weather? Was it because the battery was below 32ºF? Was it because the Voc of your solar array was too high for the SCC when it was cold?

Temps this winter occasionally dropped beneath 0 deg F

Do note that the SOK spec sheet for the 206Ah battery states a storage temperature of 23ºF - 95ºF. Letting it get down to 0ºF isn't a good idea though I'm not sure what the longterm effects will be.

 

[RaZar]

Yow!

Is there a BMS? W/bluetooth? These use power.

BMS, no bluetooth

Why only charge to 10% SoC? Your "utility" charges your battery? What is the "utility"?

It wouldn't charge any higher than 12.8v. Maybe I have the set up wrong but followed Will's advise on that. utility=shore power. Sorry for the confusion.

The BMS probably shut down due to low voltage disconnect so when you tried to measure the voltage it appears extremely low.

Could be but it took about 5 hours to charge up

That's only about 20% SOC.

It wouldn't charge any higher than that. The 12.8v was about the voltage when I first got the battery

That's under 10% SOC.


What inverter/charger do you have? Even off, many inverter chargers will have a very small idle power usage. Left like that for months it's certainly possible, especially if the battery was already pretty low.

I got the MPP Solar (its a company) 1012 (1000W, 12V) all-in-one, switched off but still connected to the battery

You should leave an LiFePO₄ battery (such as the SOK) at about 50% SOC for storage. You should also disconnect everything, not just turned off. Disconnect switches are a good idea if you don't want to physically disconnect one of the battery cables for storage.

Thanks. I don't mind disconnecting the batteries for the winter. Just didn't realize I would need to with everything switched off. Yes, I thought that maybe the low voltage reading might be due to not disconnecting.

I suggest fully charging the battery to 100% SOC and then seeing how it performs. Do you have a shunt that shows you the actual SOC of the battery? If not it would be a good idea to add one to your system.

The battery doesn't seem to want to charge any higher than 12.8v. I think it was at about that when I bought it. I do have a shunt, but I also check it with an external meter

Why wasn't your solar connected in the colder weather? Was it because the battery was below 32ºF? Was it because the Voc of your solar array was too high for the SCC when it was cold?

Solar was new in the Fall and didn't have time to connect it before winter set in (no heated space to work in).

 

[rmaddy]

The battery doesn't seem to want to charge any higher than 12.8v.

How are you trying to charge it? Are you using a LiFePO₄ friendly charger? What charge settings are you using (voltages/current)?