This fun feature can be found in a few of Makita's battery chargers, such as the 18V LXT Rapid Battery Charger and the 40V XGT Rapid Charger. It does not come in the 12V CXT charger. That said ...

[Eggmont] was facing this dilemma with a Makita battery from a broken angle grinder and decided to make a USB charger out of it. [Eggmont] took the simplistic approach, using an old cigarette ...