Hermes – Auxiliary Battery
When we decided to go with a pickup truck vs a Sportsmobile for our overlander we knew we had to determine how to run auxiliary power to the bed of truck to sustain a refrigerator, light and inverter without risking the main battery power. After a little research (youtube and 4×4 forums) I determined the best combination that suited our needs and felt secure. I decided to go with breakers vs fuses so we would not have to depend on fuses throughout a trip such as this. Breakers, although a little more expensive, meant a little more reliability. I purchased 25 feet of welders 4 gauge cable to assure a thick, durable outer liner and an extra few feet so I could wire an in-dash battery disconnect with key to shut off all power to the alternator as a second layer of protection for vehicle security. I installed a battery isolator to ensure when the vehicle was off it would not drain the main battery. There are several types of isolators and from what I can tell it’s a personal preference on which model/type to install.
After determining the schematics of the system, I needed to figure out a way to secure the auxiliary battery in the bed of the truck so it would maintain a good ground connection, not slide around and maintain accessiblity in case repairs or troubleshooting became necessary. For this I created a battery ‘box’ to securely contain all the components. Honestly, I looked around the garage for scrap wood and built a quick small two sided box. Once I secured the breakers, isolator and battery within I installed it into the back passenger side of the truck bed close to the drain hole so I could feed the 4 gauge main battery line up with ease. The inverter connects directly to the battery however I wired in a small 4 point fuse box for the DC power outlets and LED truck bed light (yes I brought a bunch of fuses just in case but can rely on the inverter if I have to go without).
We are attempting to be as self sufficient as possible so by wiring an auxiliary battery it also allows you to be able to give yourself a “jump start” by by-passing the isolator and starting our truck off of the auxiliary battery should that scenario ever come into play.
Choosing a battery to use was a quick and painless exercise of going to an RV shop and picking up an oversized deep cycle marine battery to allow complete draining of the battery without compromising the integrity of the recharge as you do in an ordinary car battery.
The refrigerator was a challenging decision for us because we were trying to stick to a tight budget so I went with a Coleman powered cooler the first time around. I designed the sleeping platform around the dimensions of the Coleman cooler so it fit nice and snug with some breathing room for the fans. Once the platform bed and cooler was installed we went on a ‘test run’ camping trip to Wyoming to work out some ‘bugs’. Come to find out the Coleman cooler running at 4 Amp/hr peak drains the marine battery very quickly, as in just a few hours. A little Coleman powered cooler was definitely not going to work for us so after much research into alternative solutions I went with a Dometic CF-40 portable refrigerator that pulls .6 Amp/hr. After some minor adjustments to the platform bed to install it properly it fit much better, kept a constant cool temperature and most importantly lasted for several days without having to recharge the Aux battery.