The answer until now has been carrying around spare batteries or maybe the USB rechargeable batteries like the Powermonkey, or just pray that you may be double quick last call at one bar of battery juice.
Rechargeable removable built into the back of the bag are rated at 3000mAh, which gives about two charges full smartphone like the iPhone. There are three power connectors, all of which can be used simultaneously; two devices cost in the lungs two shaped pockets in front of the bag (an Apple and micro/Mini USB connector), along with the USB socket on the main bag designed for non-standard connectors or for charging internet t.