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

How can I make the USB ports hot when the vehicle is shut off? Sajeev answers: The easiest answer is to not do that. Instead, consider adding USB charging ports to your cigarette lighter.

Doing this for extended periods can drain your car's battery ... as this 130-watt charger from Ugreen or a 65-watt option from Aukey. They plug into your car's cigarette lighter, letting you ...