When I was in the service, I used to dream about something like the Protonex Squad Power Manager (SPM). I hated seeing all of those half expended batteries in a stack against the wall doing nothing. This thing does exactly what the name says and with 6 universal outlets, you can manage power to multiple devices and well as recharge and harvest power to and from your batteries.
Manages and prioritizes battery usage
Powers man-packable gear
Recharges military and commercial batteries
Optimizes solar/alternative power sources
Monitors power sources and loads, alerting warfighter to problems
Dynamically adjusts to changing mission needs
Smart Cable ID configures ports automatically
Provides graphical display to show power trends and permits advanced configuration
These diagrams give an idea of how the SPM can be configured to power multiple devices or to recharge batteries.
Here is a short video from Warrior West on the SPM featuring Jeff Williams from Protonex.