Aukey® external battery 12000mAh, external charger / external battery mobile dual USB, 5V / 3.1A emergency charger for iPhone, iPad, Samsung Galaxy and other smartphones, mobile phones etc. (BLACK) (Electronics)
Autonomy is considerable, its cooldown meanwhile is very long 24H around. That said with a simple phone charger that is normal. That's what I recommend you buy a charger delivering a power of at least 5V 1000 mA (1A) for batteries with intensity (A) more than 10 000 mA (1Ah); therefore your battery will charge faster.