It plugs into any device with a mini USB port either to recharge the host or provide current immediately. The P790 is a 1700mAh rechargeable battery with a USB port on top and can also be used to charge up that handheld, Bluetooth headset, MP3 player, PDA, GPS unit or whatever else it is you might have that could use a quick hit of juice. Easy to use! Simply charge up the P790 at home or work and it's ready to be hooked up to your phone when the handset's battery runs down. A great alternative to switching batteries or carrying an AC adaptor with you.