Easiest way to balance charge them would be to use battery holders so you can take them our separately and charge them elsewhere. You could use a buck converter to change what your cell configuration is, since the input and output voltages are adjustable, and tune in your output voltage, which you could then change if you ever wanted to charge a different laptop. As for how to charge them, burying several TP4056 lithium ion charging circuits makes it a lot easier. If you want to power multiple on one USB adapter, just solder the power terminals for them in parallel on the charge circuits.