Auxiliary battery for cargo trailer dome lights

[lostcause]

For those times when I need to work inside the trailer when it's not hooked to a running vehicle I want to set up an auxiliary battery to power the dome lights. The trailer has two dome lights now and I may add two more. I'm not looking to run these non-stop, but for an hour or two here or there when needed, and although I haven't dug up the specific draw yet, they are LEDs so they aren't going to consume a lot of battery power. I was first thinking about a lawn & garden battery, but i'm now thinking about a breakaway battery since you can get a complete kit with battery, box, charger, and even the breakaway switch for about $35 delivered (i'll be ordering a new breakaway switch when i redo my open trailer this summer anyways, so it's a bonus).

There's plenty of room in the nose with the breakaway and junction box to add another battery, and I'm thinking the easiest path to do this would be to just add a DPDT switch in for the lights so i can choose between vehicle or onboard battery? i'd like to have it all wired so i don't have anything manual to do, but everything leads me back to thinking there will be an issue cutting a battery into the aux line in the junction box because that is the line that would also power the battery charging circuits.

Someone here must have done something similar?

 

[4570Man]

I just bought 2 battery powered work lights and stuck on the ceiling.

 

[lostcause]

seems kind of redundant since i already have lights on the ceiling, plus small batteries (AA/AAA) don't always fare well around here at certain times of the year. my luck they would be dead when i needed them. even lithiums don't always work well in the cold till they thaw some.

 

[Xfaxman]

What I did back before LEDs was wired a trailer receptacle in a 12 volt AC outdoor lighting transformer.

You could use a 12 volt DC power supply if parked where there is AC available.

 

[rusty842]

Is the AUX always hot??

Look into a battery isolator. Had a truck that had one. Allows the truck to charge the aux battery buy won't drain the main vehicle battery when using accessories.

You could use your AUX power to charge the trailer battery.

 

[RustyA]

Any battery you install in series will be charged by the tow vehicle. On my wife's horse trailer I installed a deep cycle RV battery in series as it's more tolerant to multiple discharge cycles.

 

[KennyG]

How much room do you have? My solution to this in the past has been to find the oldest battery I have in a vehicle, buy a replacement, and then use the old one as an utility battery. Cost is about $8 to forgo the trade-in, and an old 12v battery will last years in this kind of service.

 

[grsthegreat]

on my 30' 5th wheel horse trailer, i wanted the interior lights to work when trailer was unhooked from truck. i built a battery box with manual disconnect to kill it when in storage. works great. recharges when hooked up to truck thru trucks wiring. mine runs 12 separate lights. im sure yours would work fine. you can swap incandescent lamps for leds also. fit in same socket. mine also operates the hydraulic landing gear.

 

[PILOON]

How much room do you have? My solution to this in the past has been to find the oldest battery I have in a vehicle, buy a replacement, and then use the old one as an utility battery. Cost is about $8 to forgo the trade-in, and an old 12v battery will last years in this kind of service.

LOL,
when I drove company cars ('50, '60's) I replaced @ 3 years as the battery cost was less that a service call plus I had that waiting time to make productive sales calls.
When it real cold a typical service boost call could take 5-6 hours.

Back then they had those devices that started your car every 3 hours to keep it warm.
On those cold nights you never booked a floor level outside room at a motel with a dozen or so cars starting every odd 1/2 hour.

BUT I always kept those battery 'pulls' for my toys.

 

[4570Man]

seems kind of redundant since i already have lights on the ceiling, plus small batteries (AA/AAA) don't always fare well around here at certain times of the year. my luck they would be dead when i needed them. even lithiums don't always work well in the cold till they thaw some.

I bought 2 of these lithium battery rechargeable lights for like $20 each and they’re magnetic for easy mounting. Admittedly I don’t do much in the cold and I don’t live in a climate as cold as yours but I’ve never had any problems with them.