The circuit diagram of the Arduino-controlled 12V automatic battery charger is shown in Fig. 1. It is built around Arduino Uno (Board1), adjustable voltage regulator LM338 (IC1), 12V voltage regulator ...

The Milwaukee M18 Dual Bay Simultaneous Super Charger has slots for two M18 batteries and claims a sixfold increase in charging speed, powering an M18 6.0 Ah battery to 80% in just 15 minutes.