Working on a build now and thought I'd post what I've started. The main use for my box right now is to power the lights on the home-built camper I made, but I'm building it in mind with the possibility of bringing it on the river. With all the things I'm adding to the outside it probably won't be dunk-proof, but it will certainly be splash-proof.
The battery is a 33 Ah sealed lead acid battery. I don't think it qualifies as a true "deep cycle", but since I rarely foresee going anywhere near completely draining it I think it's a non issue. It's the SLA12-33 from this table, and I bought it at a local shop. It's non-gassing, maintenance-free, and safe to operate in a completely sealed enclosure (though I intend to open the lid when I'm charging it).
I could probably fit 1 size larger in there, but this gives me room to work with and keeps the battery out of contact with the box itself, which I like.
I bought a NOCO Genius 1100 to charge it...
G1100 | Genius Battery Chargers
The box is an ammo can I bought at Princess auto in Canada... a fat 50 cal...
PA-108 FAT 50 Caliber Metal Ammo Box | Princess Auto
When I silicone in all the fittings it should be very waterproof (i.e. rain and splashing), but probably not fully dunk-proof. In the picture Iím just giving the initial charge to the battery with the alligator clips for now. I was thinking about attaching a ring terminal lead to connect to, but I might actually not bother with that and just do it this way when charging at home. Iím still going to permanently attach a harness that connects to my solar charger via ring terminals that will stay in the box with everything else.
On the bottom Iíve got some wood that I cut to size thatís intended to keep the battery in a stationary lateral position, and thereís some strapping Iím going to run over top of it to secure it in place when the battery is done charging. The wood is epoxied in to the base of the box so it should stay put.
You can see the trailer wiring harness roughed in and not attached. I still need to make sure I put the hot wire to the correct tab in the trailer wiring connector (I only want to power 1 wire of the 7). Itís not 100% clear to me which wire it is thatís powering the lights in the trailer and Iím going to test it before I seal it all in. Iíve look at wiring diagrams online and Iíve taken the parts of my trailer apart that I can to easily see how theyíve wired it and the only conclusion I can come to is that I donít know what theyíve done but it's not standardÖ so Iíll test.
The rectangular hole is for a digital voltage read-out that Iím going to install. Ordered it a while ago on Ebay and itís supposedly waterproof. Something like this, but I paid much lessÖ
5pcs 0 56" Waterproof Voltmeter 4 5 150V 12V 24V 36V Voltage Panel Meter FOR CAR | eBay
On the opposite side of the trailer connector and voltage read-out Iím going to put thisÖ
Waterproof Motorcycle USB Cigarette Lighter Power Port Outlet Socket SH HOT | eBay
Ö which Iíve ordered, but itís coming from china and it wonít be here for a while. Thatís more for versatility than anything, because this will mostly be used for the trailer using the connector in the photos. It will at least give me the option to use it to do other things (like on the river, perhaps) like charge my phone or plug in an inverter or something. Most builds Iíve seen online have multiple 12v outlets and/or multiple USB power ports, but I really donít feel like thatís necessary and it just clutters up the work area in the ammo can. I can always get a splitter for those ports if I find the need to use more than 1 at a time.
About a year ago I got a solar panel on sale and itís 40 watt (so up to about 3A) which is actually stronger than the AC charger I bought, so it should charge the battery pretty quickly under full sun. In fact, I wonder if that slightly unregulated and ďdirtyĒ power might not be great for the battery (at least, relative to the NOCO charger)? One nice thing about that NOCO charger is that itís intelligent and changes the current itís putting into the battery to preserve it and can also be left connected indefinitely since it will not over charge. The solar panel comes with a charge controller but who knows what itís doing, and itís probably not as much as the home charger. The panel it's big and rigid and not suitable for the river, but would be useful while camping. If I think I'll need supplemental power on the river I'll look into a smaller folding solar panel.
Iíve thought/stressed about the best way to do this for a while and it feels good to have made the financial decisions and start the build. Iíll most likely be camping next weekend so I can try it out.
The extra image at the bottom is a charge that shows voltage vs. charge level at different temperatures. I'm going to tape this on to the box somewhere since I'l likely be camping into the fall and it will be useful to know much much power I still have left based on the voltage read-out.