With the T-Mobile Sidekick 4G Naztech 1900mAh Emergency Back-Up Battery, you will never find yourself without a full life of battery. The back up battery is small and compact, allowing you to place it in a pocket or purse. The T-Mobile Sidekick 4G Naztech 1900mAh Emergency Back-Up Battery, you can be sure to avoid missing any important phone calls because your phone died. All you have to do is plug in your T-Mobile Sidekick 4G and the Naztech 1900mAh battery does the rest.