Originally Posted by Paxman
Itīs most definitely wired in series. The 18650 LiOn cells are 1,2 V and since USB is 5 V you need to connect the cells in series: 1.2V X 4=4.8V. The regulator probably step the voltage up .2V and also keep the voltage up until the cells are completely empty since the voltage normally drops with usage.
The capacity is depending of the LiOn, if they are say 1500 mAh each the pack will also have 1500 mAh. If you want 4 X 1500 mAh (5000 mAh) you connect the cells in parallel but then you would only have 1.2V.
Easiest way to get more capacity would in my opinion be to splice in a battery connector between the camera and the battery pack. This way you can have several batteries and as high mAh as you want!
LION's are 3.7-4.2v
Pack is parallel wired, so it stays 3.7-4.2v, and you add up all mah of batteries.
Has DC-DC booster to take it up to 5v for usb out connector.
Link to second one I showed takes 9v input to charge, which is right for the 2 paralleled cells.