The Ricoh Theta S is unusually fussy about charging. In my experience, your results may vary with anything except a high quality USB charger, 2A minimum (I use a 2A iPad charger). Also, if the battery runs out, it can be difficult to recharge. Theta S cameras that won't recharge are often interpreted as "damaged", and there is no proof that there is any actual damage. My advice is to use a high quality USB adapter, minimum 2A capacity and a good quality USB cable that uses all 4 pins (not a "charge only" cable). It is OK to use a higher capacity quality charger as the Theta S will only use the current from the charger that it needs.
A USB battery pack can be used to operate a Theta S for extended periods. Some battery packs will turn off while in use...I suspect that the Theta S is not drawing enough current for the battery pack to detect. My solution is to use a Porta Pow Battery Monitor. The Porta Pow is connected in between the Theta S and the battery pack, using the "No DATA + Smart Charge" USB jack. Now the Porta Pow is in charge of regulating current to the Theta S. Cost is about $12.
The Porta Pow is also great for finding the charger that works best with your USB powered device. The display indicates how much current is being delivered.
