The British army has begun issuing Soldier Portable Charger (SPC) units to eight man infantry squads, as well as smaller, and lighter, batteries for radios. The SPC weighs less than a kilo (2.2 pounds) and, with its fold out (one square meter/10 square feet) solar panel, troops can save up to 30 kg/66 pounds of batteries that have to be carried on a 40 hour patrol. The SPC allows transferring power from empty batteries (which still have a 10-20 percent charge) as well as getting juice from vehicles.
The U.S. Army has also been using devices similar to the SPC, as well as similar folding solar panels (including small ones that can be draped over the back of your pack while on the move.) Batteries are a growing problem as troops receive more electronic equipment. The weight of batteries, and needed spares, continues to grow. Fuel cell batteries were to have solved the problem, but small fuel cells for infantry use have not shown up yet.