I have lots of small (500mAh) LiPo cells taken from Vaping devices (eCigarettes). I want to reuse them in some consumer electronics devices that run off 2 AAA batteries. There is generally space inside the devices to add extra cells/circuit boards so I'd like to add as many cells in parallel as will fit and charging circuitry preferably with a USB port.
Should I stick to parallel cells only for simplicity? I understand that before connecting them it's best to get them all to the same voltage and bottom balancing is better than top. What's the best way to charge/discharge them to exactly 2.5 volts?
Is a TP4056 (with protection) the best board for integrated charging?
I understand the LiPo cells go from 4.2 to 2.5 volts and I need 3V so maybe I could use a buck converter or low-dropout regulator to power the device.
I'm not concerned about charging and powering the device at the same time (power sharing).