Right now, the socket can store about 1,000 mAh (amp-hours, a unit of charge), which is enough to keep a 60-watt light bulb lit for about 20 hours. It's not quite enough to fully charge a dead iPhone, however, since the iPhone 5 features a 1,440 mAh-capacity battery, and the iPhone 6 Plus battery needs 2,915 mAh.