I was having a discussion with a buddy of mine, and he mentioned an outfit that was selling a waterproof battery pack in a hardened package. It used a 12v 5ah NiMH battery pack, and included a waterproof 12v power port. At an asking price of over $220, I felt this was a ripoff, but the concept is valid. I knew I could design a better solution, so I came up with a 10ah, and 20ah version, for about half the cost, with some nice options like built in usb ports (cellphone, mp3, and kindle charging) and solar recharging.
So Here Goes:
One surplus ammo can, water proof, can hold two 12v 10ah battery packs (20ah total)
One 8 D cell holder (12v) (get a 10 cell holder if you can find one, or just add a 2 cell holder in series), add a second set for 20ah capacity instead of 10ah.
One set of eight 10ah NiMH D cells + 2 more for 12vdc (second set for 20ah). Alkaline D’s are 1.5v (8 = 12v) but NiMH are 1.2v (10 = 12v).
One marine waterproof 12v power port (can connect the solar panel here for charging, or add a second one)
Optional waterproof dual usb charging port
Optional 40 watt solar panel (add a second one for the 20ah solution).
Optional second ammo can to hold a 150 watt inverter until it’s needed for low wattage ac gadgets, like a laptop or portable tool charger.
As long as the charge rate is C5 or greater, you don’t need a charger, as solar is only going to charge 3-5 hours full sun daily anyway. A 10ah battery / C10 = 1 amp charge rate. Divided by C5 = a 2 amp charge rate.
You could also add a 1amp 12vdc power pack for ac charging. Charging at higher rates than 2 amps require temperature monitoring and a smart charger, which we will be building at http://arduinotronics.blogspot.com