Portable Battery Supply

Readers of this blog will no doubt remember the "Mobile Battery Cart" - indeed the post before this one is a short update on that. For some time I have been thinking of a portable unit I could take in the car, on a bike/motorcycle, or even pack in a suitcase for travel. Hardened Power Systems makes a particularly elegant system they call their "Juice Box" that is built into a US Army ammo can and is waterproof when the lid is closed. It features a 30 amp-hour lithium ion battery, digital voltmeter, USB output ports, Anderson power pole connectors, an integral power inverter as well as a 12 volt "lighter" socket. It's a sweet system - the main issue with this is at $580 it is well beyond my budget. But ... all is not lost.

At the battery shop where I work part-time, we recently scrapped out a small "MAC" type (NOT related to Macintosh computers) battery charger. The case was quite pitted with oxidation and even though it was otherwise in good condition, the boss said it wasn't worth keeping. So I asked for it, explaining what I wanted to do with it, and he kindly gave it to me. See the top photo. It has a handle on the top and plenty of room inside for two 12 volt/7 or 9 amp-hour SLA or AGM type batteries. There is room inside for a low voltage cutout board like I built into the mobile battery cart, a digital panel-mount voltmeter from eBay, a solar charge controller and perhaps a small power inverter in the 100-200 watt range.

The second photo shows it open with two AGM type batteries sitting inside. Note the rust and corrosion on the inside metal transformer support rails as well as on the "feet". I'll sand and treat those areas with rust remover solution, then I'll sand the whole box with fine grit sandpaper, then paint it inside and out with car engine enamel. I've used that before on past projects and gotten excellent results in terms of looks and durability. Obviously I'll need a front panel made of aluminum or plastic to cover the holes in the existing panel.

Some 5-way binding posts on the front panel might be useful, too.

Once built, my 5-watt solar panel should be able to keep this charged when traveling or during emergencies. A unit like this could charge cell phones, maintain LED lighting, or power my VHF radio and/or a portable shortwave radio for considerable time on a charge. While it is NOT a "juice box", it will serve the purpose well enough for me - and at a fraction of the price. I'll try to post updates of this project as it proceeds.

I hope this gives readers some ideas for solving their own portable or backup power issues. Please feel free to write back with your own ideas!!