A Simple 12 Volt Battery Pack.

You can make your own.


A friend of mine made some battery boxes using 50 cal ammo cans and 12-volt burglar alarm batteries.  They are very nice compact units that will provide 14 amp hours of power.  I have built a couple of them and they work well.  I have used them to power 12-volt lights, but they have many other potential uses.

What they consist off is a 50 cal ammo can in which you drill a hole for the female half of the cigarette charger.  The hole should be about 1 ½ inches from the top of the can.  You then take two 12 volt 7 amp hour batteries and wrap them in Saran wrap.  Place the Saran wrapped batteries in the can next to each other.  Fill the can with spray foam insulation.  It comes in a spray can and you can get it at Home Depot.  You don’t want it to cover the batteries, just hold them in place.  The reason for the Saran Wrap is so that in the future you can exchange the batteries without removing the foam.

12 volt charger

Now complete a simple parallel circuit running from the two batteries to the cigarette charger.  Place a 15-amp fuse in the hot side (the red wire) just before the charger.  There are a couple of different ways in which you can charge the box.  One way we have used is to take an old 12-volt wall charger and attach the male half of a plug that will fit the cigarette charger.  The second way is to use a solar charger.  To preserve the maximum life of the batteries the rule of thumb is to never charge more than 10% of the charge of the battery.  In other words, these two batteries total 14 amp hours, so you should never charge at a rate of more than 1.4 amp hours.  This is about a 20-watt solar panel.  If you are using a bigger panel, you will need a controller.

In this view you can see the entire simple circuitry

We are currently working to improve these units, if you have any suggestions they are welcome.


11 thoughts on “A Simple 12 Volt Battery Pack.”

  1. That’s a neat setup. 🙂 I do have a suggestion, though; instead of using the red box blade connectors, solder the wires together and use shrink wrap to seal the connection.

  2. Good article. We created a similar setup, but already has the charge controller and solar panels as part of the system. I am posting the links so you can see it, not trying to get a free website plug.

    I like the idea of the saran wrap. I recently converted a large toolbox to accept a 100AH battery, using cardboard as my barrier. Thanks for the idea.

    You can see our original article here: http://www.prepperlink.com/index.php/prepare/energy/item/57-solar-project-ammo-can.

    Additionally, we just released a new one which provides a little more capability. http://www.prepperlink.com/index.php/prepare/energy/item/60-enhanced-small-solar-power

    Both have step-by-step guides.

  3. As an electrician, I would not seal any lead acid type batteries in foam or other plastic. All lead acid batteries offgas hydrogen and should have ventilation. Also batteries get hot and could catch fire if sealed in a box too well.

  4. I forgot to mention that I always leave the lid open when I charge the battery. So far out of several we have made there has been no trouble with heat. I will give your points some thought.

  5. Prepper Link, that is a bad ass article you posted. I’m going to build it out this weekend. Thanks for the good ideas, Howard.

  6. As an electrical inspector here’s my two cents,
    It looks like you used standard spray foam to fill around the batteries, please see the warning for this product below:

    6. Cured foam is combustible and will burn if exposed
    to temperatures above 240°F (116°C). Do not
    apply GREAT STUFF™ foam around heaters, high
    heat lamps or recessed lighting fi xtures, radiators,
    furnaces or fi replaces where it could contact heatconducting
    surfaces. Do not use GREAT STUFF™ foam
    inside electrical boxes.
    You have a great idea, it just needs to be executed safely.

  7. A friend of mine recently constructed a similar pack using a plastic container which resembles a 5.56 ammo can. It is lighter, still rugged, and not conductive so there is less danger of shorting the batteries. He drilled a couple of vent holes in case the batteries should malfunction. The batteries fit snugly and he used double face foam tape to anchor to the walls of the box. I just found these boxes online so I am going to do the same.

  8. Forgive me but I am disabled
    My concerns are different I need back up power for a Oxygen machine a nebulizer short amount of time 15 to 20 minutes twice per day pulling 30 Amps total five to six hours of sun between my needs

    I have no way to travel different locations to collect the items to make these battery boxes no driver license /no car or truck live in the suburbs where you are charged if the grass is over six inches

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