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Problem charging LiPo battery in parallel

Tesla

New Member
Joined
Sep 28, 2020
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3
I'm planning to make a backup power system for some projects which runs on 5v. I have 12 Lipo batteries of 10Ah each. All the cells are brand new with <5 charge/discharge cycles each.
So I've attached all of them in parallel (1S12P; 3.7v, 120Ah) and used a boost converter to get 5v out.

Now the problem is when i try to charge the battery pack, it wont go above 4.04 ~ 4.06v. The charger would charge for hours and hours at 500~700mA. But battery voltage doesn't go up.

Its not the charger fault, I've tried 2 other chargers and get same result. I've also tried to disconnect the boost circuit and charge but it didn't help either.
However if i charge each cell individually then they get to 4.20v easily.
Now as u have guessed, its not possible to charge every single cell individually every time i have to charge the pack.
What am I doing wrong here? Why can't I fully charge the battery pack when they are in 1S12P?

Any suggestions would be highly appreciated :)
 
I'm not sure but if you have 120 Ah battery and charge at.. 0.5A it would 240 hours or 10 days. Admittedly I do not know where the bulk of energy is in these cells but. I suspect you need more energy in to the cell than you think.
 
Sorry if i sounded like I'm charging at 500ma but I'm not. I was charging at 15amps. But slowly as the voltage of the battery rose the amps got lower and at 4.05 volts its stuck at 0.5amps. The voltage should rise to 4.20 volts but remains stuck there even after several hours.
Why doesn't it get fully charged?
 
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