Long times on 3,3V per cell in winter months

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Dec 20, 2018
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There will be a long period in winter months, about three months, where my powerwall will have to stay at 3,3V per cell. Is that bad and should try to keep it in higher voltage?
 
If they are LiFePO4's, that should be fine. But if they are the other chemistries, you might want to bump them to 3.7V for long term storage.
 
No Lithium Ion. I think its better and either way no problem if i do so. There would not be much energy i can store in this time. Will see if everything is running. Thanks Korishan.
 
3.3 Is not a problem on LiIon either.... Questions is just why to drain them that low :p
 
Ok, always thought 3.7V-3.8V would be perfect.

Another question 3.3V would be equal to about what DOD? 90% or 80%? Does this depend on the used cell?
Also 4.0V would be what SOC?
 
3.3V is maybe 3% State of Charge? It's very low. If you do store your battery at this voltage, make sure to disconnect any loads, especially if using a high-powered BMS. Even a 1 miliamp draw will eat more than 2 Amp Hours over the course of 3 months.
 
Problem storing that low is that you have no capacity left... = YOU MUST crosscheck the cells every other day. Because there is no headroom with capacity just slightest self discharge will drain them to dangerous voltages below 2.5-2.8v. Thats also one of the reasons you shouldnt store them long term unattended at that low voltage....

I dont recommend storing it like that for any period of time unattended. You save more grief going up above 3.6V. Of course once again with no load.
 
What's more useful during winter, an empty powerwall / pack or an at least half charged pack, just in case ?
 
If these were my batteries I would store at the nominal voltage of about 3.6-3.7vdc

That said, if you dont have enough panel or power coming in the charge them up, I would just connect a variable DC power supply or an RC charger and just bump the pack voltage up using mains power.
 
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