Charging lithium batteries safely Testing the module, 3 18650s charged to 4.18v I needed a PCB module to charge four 18650 lithium batteries for my (battery powered) tube amplifier. I ended up making two different versions of the module, the first design was too compact and got a bit toasty. The second version has more heatsinks and is wider but still reaches 70°C, I could reduce the charge current but decided that if I reduce the supply voltage from 5v to 4.55v, this reduces the max power dissipation by about 0.25W.
Just some random circuits that I've built.