I'm going to make a 5v backup power source for a few of my projects. I have 12 Lipo batteries(
https://www.apogeeweb.net/electron/the-best-guide-to-volt-battery.html), each with a capacity of 10Ah. The cells are all brand new and have only been charged and discharged five times. So I connected them all in series (1S12P; 3.7v, 120Ah) and used a boost converter to get to 5v.
The issue now is that when I charge the battery pack, it only reaches 4.04 4.06 volts. At 500-700mA, the charger would charge for hours and hours. The battery voltage, on the other hand, remains constant. It's not the fault of the charger. I tried two additional chargers, and each produced the same problem. I also tried unplugging and recharging the boost circuit, but it was ineffective. However, if I charge each battery separately, they quickly reach 4.20 volts.
As you may think, I can't charge each cell individually every time I need to charge the pack. In this circumstance, I'm not sure what I'm doing wrong. I've read the battery instructions, but I'm still puzzled as to why I can't fully charge the power pack when it's in 1S12P mode.