A friend of mine used to have a work cellphone for which she only had a car charger. She used to just leave the phone plugged in to her car’s power outlet at night to keep the phone charged, but she ran into a problem when she bought a new car that didn’t supply power to the outlets when the engine was off. If she’d had the 5 Amp AC to 12V DC Power Adapter from ThinkGeek, she wouldn’t have had a problem. With this adapter, you can power any car gadget, like a GPS or heated seat cushions or even a USB charger, using your house outlets. The adapter converts 110V AC power from the wall into 12V DC power, and it is rated for a 5A load. It’s $19.99.