This is a piece of gear I've never really seen in an overland load out but I feel would be extremely useful and it could definitely save you from being in a bad situation if the need arises. 
I work as a mechanic daily so I spend lots of time on tool trucks, that's where I found this little device. It functions as and external battery pack for numerous different small electronics and lights, can jump start a diesel truck, and even has a small(albeit not very good) flashlight built in. It has two USB ports in the top to charge anything with a USB plugin as well as a 19v plug in the side.
Even the 110 wall charger is well though outvwith two USB ports, you can plug both charging cable into the outlets and the battery pack itself, or charge the battery pack and another phone, camera, etc. with a 12 month charge hold you can charge it fully before a trip and toss it under the seat until you need it and it will be ready. This is the second generation with considerably better build quality and they improve the battery clamps. It's still a little on the plasticy side in my opinion but it's a lot more robust than the previous generation. 
My main complaints are the pretty much useless flashlight(I'd rather it just not be there or have another USB port), and the clamps can be a little finicky because they have a safety feature built in to keep you from trying to run a vehicle with no battery on the battery pack and frying it. At $239.99 it might be a little more than some are willing to spend but I say the cost is very justified the first time it gets you out of a bad situation that would have left you stranded otherwise. 
(Coleman propane bottle for size reference)
I work as a mechanic daily so I spend lots of time on tool trucks, that's where I found this little device. It functions as and external battery pack for numerous different small electronics and lights, can jump start a diesel truck, and even has a small(albeit not very good) flashlight built in. It has two USB ports in the top to charge anything with a USB plugin as well as a 19v plug in the side.
Even the 110 wall charger is well though outvwith two USB ports, you can plug both charging cable into the outlets and the battery pack itself, or charge the battery pack and another phone, camera, etc. with a 12 month charge hold you can charge it fully before a trip and toss it under the seat until you need it and it will be ready. This is the second generation with considerably better build quality and they improve the battery clamps. It's still a little on the plasticy side in my opinion but it's a lot more robust than the previous generation. My main complaints are the pretty much useless flashlight(I'd rather it just not be there or have another USB port), and the clamps can be a little finicky because they have a safety feature built in to keep you from trying to run a vehicle with no battery on the battery pack and frying it. At $239.99 it might be a little more than some are willing to spend but I say the cost is very justified the first time it gets you out of a bad situation that would have left you stranded otherwise. (Coleman propane bottle for size reference)
