I wanted a good way to charge my LiPo batteries in the field without being dependent on my vehicle’s battery. After searching through RC forums for guidance I found that many people focused on getting the largest amount of charging capacity available per dollar. Coming out on top with that criteria were deep cycle marine batteries. The EverStart Maxx Deep Cycle 125 Ah battery costing ~$100.00 is a common recommendation for getting the most capacity/dollar.
I currently fly small foam airplanes and a mini quad so my ideal charging solution is not a large 60+ lbs (~27 kg) lead acid battery even if it is the most bang for my buck. I’m not going to haul around such a heavy battery given what I fly. After thinking about my average flying time and the typical batteries I needed to charge, I came up with the following requirements for my field charger:
Not extremely heavy or unwieldy to carry
Decent battery capacity so it can charge ~6 1400Mah LiPos before needing to be recharged
I can use it not only run my LiPo charger but also charge USB devices
I can easily see the source battery capacity and know when I’m getting close to 50% discharged and I need to recharge
With a little bit more research I found that for those wanting a lighter solution, car jump starters were recommended. Here are a few examples:
These are definitely light and portable but I was not sure how well a lithium ion battery would hold up over time or if they were deep cycle batteries. Since I wasn’t very confident in these I decided to build my own charge box with a sealed lead acid battery that would have less capacity but would be lighter than the large marine batteries.
Finding the battery I wanted to use was pretty easy. For ~$37.00 at Amazon I found a 18Ah deep cycle sealed lead acid battery that weighs 12 lbs (5.4 kg)
Finding a box to put this battery in was a bit more difficult. After running around to a few stores, trying unsuccessfully to modify a Plano tackle box, and looking online, I finally found the Flambeau Outdoors Dry Box with the proper dimensions.
With the base requirements out of the way I picked up the other items I wanted:
With a bit of measuring cutting and gluing this is how it turned out:
Charging Box ~$40.00
18Ah Battery ~37.00
- Flambeau Outdoors Dry Box Storage $12.00 (1 box) http://www.walmart.com/ip/21854607
- 18Ah Deep Cycle Sealed Lead Acid Battery $37.00 (1 battery) 12 lbs http://www.amazon.com/gp/product/B001DL7D1O
- Momentary Push Button Switch $2.50 (5 buttons) http://www.amazon.com/gp/product/B0094GRZPE
- Dual USB / Lighter Socket $12.00 (1 socket) http://www.amazon.com/gp/product/B00LULJIW4
- Banana Plug Jack $8.50 (10 jacks) http://www.amazon.com/gp/product/B00D6AICR4
- Battery Capacity LCD Indicator $5.00 (1 indicator) http://www.ebay.com/itm/12V-24V-36V-48V-Battery-Capacity-Tester-Indicator-For-Lead-acid-Lithium-LiPo-LCD/141525042202
Edit: Multiple folks have requested pictures of the wiring connections so I’ve included them below.