Got a buck? Make a charger for LiR2032 coin cells. It could hardly be cheaper or easier.

One cheap PCB from an auction site. 1 scrap bit of copper pipe. 2 bronze pennies. Put them together and charge up a 18650 Li ion cell. ...

So if you  open up a 9 V battery, you find 6 thin 1.5 V cells inside . But what was inside that lantern battery, the rechargeable PP3, or th...