You can add another rv styl battery to the engine comapartment, use it to run 12V appliances etc in the trailer along with the batteries you have in the trailer. To be frank tho, all of them, both truck and trailer "SHOULD" be the same size, age etc. If you have say 2 6V bats on the trailer, add a 12V to the truck and try to runn of of those three, it will not work. If you add a size 24 to the truck, along with 2 other 24's on the trailer, no big, this will work. Just make sure there is an isolator between the truck starting battery and the new rv/house style deep cycle battery, otherwise you can drain the starting battery along with the house batts in the trailer and truck.
I had this on an 88 with a 454, worked well. When I sold that rig and got a diesel, I did not realize how much actual extra time I got before needed to charge the trailer batteries. These three were equal to a bit better than 2 size 27 batteries, not as good as 2 BIG 6V batteries I put on the tongue of my TT later.
05 Chev CC D/A LS Dooley
92 Navistar dump truck, 7.3L 7 sp, 4.33 gears with a Detroit no spin
00 Chev C2500, V5700, 4L80E, 4.10, base truck, no options!
92 Red-e-haul 12K equipment trailer
3 Single axle utility trailers
Tell us more about your vehicle, what is currently in it, what make model, and what battery, and what size alternator vs. current power load, and what loads the trailer is currently drawing from your vehicle as you are driving down the road.
I have a 2003 Chevy Silverado 2500HD with 1 interstate battery in it. In the trailer I have one battery that came with the trailer. I don't know the loads on the trailer or the alternator size. This was just a general question to find out if there was any reason that would benifit me to add another battery to the truck.
I know that with demands on power for charging iPads, iPhones, laptops, and running GPS equipment and backup cameras are high and if it would help add additional battery. Especially for long trips with the family.
All of my trucks since 91 (5 Chevy's) were ordered with the auxillary battery option. All were gas engines. The auxillary battery is seperated from the main with an isolator. The isolator seperates the the two batties when the ignigtion is off, allowing a drain on the auxillary without effecting the starting battery.
I've ran elec winches, Ham Radio gear, flood lights, campers, inverters and even pull it out for elec trolling motor in the boat. It's a ready charged 12v power source.
2012 Chevy 3500HD Dually 4X4
Crew Cab long bed 6.0 gasser 4.10
06 Hitchiker II LS 29.5 FKTS
Adding the 2nd battery would be almost as easy as going to your local dealer, or even a wrecking yard, and getting parts, a saturday afternoon putting them in etc. You could probably get the tray off of a wrecked diesel to boot!
The wiring part should be pretty easy.
My personal feeling is, an extra battery will not help in the charging of other items per say. More from a us it with the battery you have on the trailer to last overnight in colder temps etc. Which frankly, would be easier to add a 2nd battery to the trailer than the truck.
A 2nd battery in the truck does work well if you are using an electric winch, or other higher yet power need item. A portable welder is another item, power tools with an inverter etc.
You may or may not need to upgrade the alternator, which might be a better way to go if using power items as mentioned for the kids in cig lighter sockets or equal. "ALONG" with a 2nd battery on the trailer. Which if doing, might be the time at looking at going with BIGGER Ahr batteries than the one you have.