Soulra 8400 Boost USB Rechargeable Backup Battery with high performance Lithium Ion battery 8400mAh Black (Accessory)
Extremely simple, super efficient, charging is still a little slow with usb, and like the other reviewers, I deplore the lack of mains charger. The weight is also a disadvantage, but I do not know if we can do better, I have not enough knowledge abou
