iWalk Supreme 10400 Duo Black 10,400 mAh Backup Battery for Smartphones and Tablets Running out of power with a smartphone or tablet can hamper both your business and social life during a critical moment. The Supreme 10400 Duo compact backup battery is small enough to pack with your brief case or even slip into your pants pocket. An impressive 10,400mAh Lithiumion battery can easily power your smartphone and tablet simultaneously with Dual USB ports. Simply connect your current charging cable to the Supreme 10400 Duo to top off your device. Fast charge your tablet with the 2.1 Amp rapid charging port. Don't worry about leaving your tablet or smartphone connected to Supreme 10400 Duo as smart circuit protection keeps your devices from overcharging. The DC In/Out port is protected from dust with a cover to prevent unwanted interference with future charging.