I went through a number of iterations before deciding on the best way to package SLA (Sealed Lead Acid) batteries for camping and other portable power uses.
The arrangement described here is a reasonable compromise between capacity (7AH) and weight, and is also a reasonably robust and waterproof solution.
I added a 5A thermal breaker (it’s under the round white plastic cover to the left of the sockets) – this provides adequate protection against short circuits, and is much better than a fuse, which will always blow when you don’t have a spare available.
Internally, the wiring is so simple, I’m not even going to show a circuit diagram. Odd bits of foam are used to locate the battery in the centre of the case.
Parts used:
| Item | Description | Supplier |
| Case | Spelsberg 110-906 | Farnell 531303 |
| Handle | CPC EN55266 |
|
| Battery | Yuasa N7-12 | Various |
| Thermal Circuit Breaker | Tyco W57-XB1A4A10-5 | CPC FF01650 + FF00583 |
| Sockets | Cliff Touchproof 4mm | CPC CN11310 + CN11311 |
Update 2011
Since this article was written, I have installed charging circuitry in each battery which eliminates the need for an external charger. Whilst I would be happy to provide details, the charger is based on a proprietary board that is no longer available.
Update 2017
I’ve now built more battery packs to a slightly revised design. This uses a standard “cigar lighter” output socket. These are available from a number of Ebay suppliers; search for “Waterproof DC Cigarette Lighter Socket”.
To make the battery pack, the top of the case is drilled, the handle riveted into position and the outlet socket fitted:
The outlet socket needs a 29mm diameter hole drilled 22mm from the long edge and 30mm from the short edge. This position is quite critical if the battery is also going to fit! I also had to clip the lugs from the retaining nut as the socket is very close to the case edge.
The thermal breaker, charge socket and charge LED are fitted to the top:
This case has mounting standoffs in the base. These need to be cut down below the level of the “rings” around the mounting holes:
The charger board is fitted at the bottom of the case, the battery is wired, and some bits of foam installed to stop the battery moving around. Note that the battery has to be at an angle so that it doesn’t foul the output socket:
Test it all works, and the job is done!
The battery status is indicated by the LED as follows:
- Slow Pulsing Green – Battery OK
- Slow Green Flash – Normal Charging
- Fast Green Flash – Reduced Charge (Input too high)
- Steady Red – On charge, Charging voltage too low
- Steady Green – Charged Slow Pulsing Red – Battery almost flat
- Fast Pulsing Red – Battery flat – DO NOT USE
- Flashing Red – Faulty battery or battery too cold or hot.
The cost of the parts for the case, including battery, was around £50 in 2017.
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