FocusA 11200mah Portable High Capacity Dual-port External Battery Power Bank Backup Charger (White&silver) if buy 2 keyboards once time or A Keyboard plus a power bank External Battery Charger Pack Portable Power Bank for iPods, iPhones, iPads, MP3/MP4 players, PSP, NDS or any device with USB charging 4 LED light for power indicator Dual USB can charge 2 devices simultaneously Auto shut off power saving mode Safety Control Protection for over current, over charging, over discharging, over temperature & short circuit