The background is I am a cub scout den leader and I have been doing a lot of camping and hiking with both my scouts as well as my own kids.  While I appreciate that it is best to just leave the electronics at home I also need to make sure the kids are happy or they will revolt and demand more time in front of the TV or a home where they have their various gizmos.

I see this as a potential emergency item as well as frankly having a way to charge anything that can be charged via 12v including USB adaptors is a huge plus.

Project goals:

I want to make this box small and portable.  It needs to be water resistant and durable.  The primary goal will be to use it to recharge cell phones, tablets, etc., but also AA/AAA batteries and anything else where USB chargers might be an option.  I am trying to figure out how many Amp Hours I need out of the battery but from some calculations I have found online a load of 5 mA will take 200 hours (about 8 days) to drain 1 Ah from a 12v battery.  I want to get a sealed deep cycle battery for this project as clearly this is intended to be run to death if needed.  

Finally, I will add battery tender charger hookup to the battery and I will charge this with one of my several battery tenders I use for the motorcycle or other 12v batteries I keep charged for emergencies.  I plan to have at least one 12v car style outlet as well as upto four USB style outlets.  Finally, I will add a master switch to prevent the USB ports from using power when the battery is not in use and I guess a small LED to show that status of the USB Ports would be smart too.

I know the hardest decision is finding the battery.  Then finding the container that I can mount the battery in along with the modest cables and adapters that will be needed.  I have some spare pelican cases around that have not been used for a while or I can buy one that fits that need.  I know for example I have a spare Pelican 1200 sitting on the workbench that would love to come camping with me!

Anyways, it's a pet project and I will post photos as I work on it.  Biggest trick is picking what battery to use!  I need to see what I can find locally and work backwards from there but I believe anything 7Ah or larger should work for my needs.

I am sure some here have made these in the past - any tips to prevent me from relearning something you already know?  I have a pair of full sized deep cycle batteries I keep with my preps at home but they are just too big and heavy!  I want something that can be easily carried by the kids to the tent, on the kayak, or by the campfire as needed.

Thanks guys!  I didn't think of the kayak crew using these for their fish finders and lights but a quick Google search found many other examples.  I hope to work on this over the weekend.

I have wanted to build an alternator charging system like this for quite a few years.  I do have two big 110AH Deep Cycle Marine batteries hooked up to battery tenders and I have the various connectors with that kit to do the same kind of thing I want to do with this small kit - IE 12v Car Adapter with USB hookups as well as 12v LED rope light and DC/AC Inverters.

As for the suggestion to use a jump box, I have one of those as well.  The issue there is the one I have is pretty darned heavy for scouts and tent camping.  I could bring it and leave it in the truck but those batteries are a robust motorcycle battery and are not designed to be used as a deep cycle battery.  My scouts would kill a motorcycle battery if they run it dead all the time.  Now, I could swap the battery in one of those to a deep cycle battery but then it wouldn't jump a car well as it wouldn't have the CCAs required.

So, I guess I am looking for something between a consumer sized USB power supply  like this:



And the monster two wagon job above

Something like this in fact:





Just with a marine (water proof) switch to kill the power and a normal car adapter plug and USB outlets.  I was originally planning to have all the connections inside the box as I am not planning to use use this as a boat box but I may change my mind.

I realized I never came back and shared my little project.  This was super easy to do other than one major issue that I never did figure out and I will add that to the end of this post.

To build this I used the following:
1.  Pelican 1120 case
2.  8.0 AH 12v battery that I managed to get at Cabela's from their "bargain cave" cheap
3.  12b Battery Charger - again from Cabela's Bargain cave
4.  10-gauge to SAE waterproof plug
5.  Fuse holder and I am running it with 7.5Amp fuses
6.  10-gauge 2-wire SAE extension cord (Cut in half so half goes to battery charger the other half to splitter with two 12v plugs)
7.  Pair of 12v car to USB adapters

To make this all I did was first drill the hole for the water proof SAE plug then I sealed it with silicone and used aluminum pop rivets to make it solid.  Then I took the positive lead and attached the inline fuse holder and then added 1/4-inch female plugs to pos/neg lines to mount to the battery terminals.

For the charger, I simply removed the wire that came with the battery charger and used the wire with an SAE connector.  I had an old power outlet splitter that we had not been using so I sacrificed the cigarette plug and soldered the positive and negative wires to the connections.  Then sealed everything with heat shrink wrap and then electrical tape.  

I was able to charge three IPAD minis and an IPAD 2 at the same time with this setup in a test.  Obviously with the 12v sockets I have a lot of options for what we can do with this little box now.



Charger works and changes from charging to fully charged indication.


I used industrial Velcro to stick the battery to the pelican case and it works well.






The USB adapters have LEDs so I have a way to verify I am getting power to the outlets.


Note the power output cord fits in the box with the 12v to USB adapters.


Problems:  I had tried to put a switch in this little box so that I could kill the power to the outlet.  The problem I ran into was the lighted switches I was trying to use are designed to be used under load.  As soon as I would turn the switch off the switch connections would smoke.  I decided in this application the switch was more of a hassle and risk than it was worth so I just didn't evaluate it further.

Improvement idea:  I wish now that I had went with a slightly larger box so I could store the charger and other cables in this box.  It does what I had wanted it to do but for a box I don't really plan to carry around a little larger box and the ability to store the charger for this box would have been nice.  As is, I can wrap up the various phone, tablet, USB (micro, mini, etc.) cables and put them under the foam in the lid so they are always with the box to power everything and anything I might want to recharge in the woods or anywhere else for that matter.

Best Uses:  I like this for camping and that is what it was made for.  With that said, this will work great on a kayak trip, motorcycle trip, for a power outage, or anyplace else where you might want more juice then you get from a small power pack.  By far the most expensive piece was the pelican case and I could have made it out of a cheaper case but this is for cub scouts so I know it will get abused.

Anyways, thanks for the help before and sorry it took me a while to post pics of what I ended up building.

The problem is these are not deep cycle batteries - running these dead will kill the battery.  So, if you don't need to use the CCA's to jump a car it is best to use the right type of battery.