Solar Phone Charger- BLKBOX High Efficiency Solar Charger Battery Pack - 4000mAh Capacity- 2.1 Amp Output with Built-in Micro USB Cable BlkBox Ultra High Efficiency Solar Charger Battery Pack use the most advanced high efficiency solar cells to charge its internal 4000 mAh battery. Over 30% faster than other solar panels. LED charging indicators Built in Micro USB charging cable Slim Design