Revision Military, best known for their Revision eyewear, has an interesting man-portable modular rechargeable power system.
The NERV consists of a main unit, a smaller auxiliary battery which can be connected in series to the main unit.
Interestingly, the smaller batteries are designed to fit into a STANAG magazine pouch.
A potential concern with the NERV is that it's a lithium battery technology, strapped a warfighter's vest. One must remember that warfighters are also walking around with grenades strapped to them too, so this isn't a particularly worrying issue.
-- Sean Newton - 15 Nov 2016