First, a little background to this project. We have been camping for a few years in our Camp Inn, using our Dometic refrigerator in our Nissan Xterra, plugged into the factory outlet in the back and it has served us well. However on a recent outing in Sequoia National Park, we went on a hike one day directly from the campground without starting the car for a full day. In the morning, the battery was low enough it would not start the car. We had done this before, but this time the battery couldn't take it. Luckily we were camping with my son and his family and a quick jump and we were going again. However, if we had been out in a remote place (think Death Valley) by ourselves, it would have been a big problem. The battery in the car was only 3-1/2 years old, but although it was a high quality AGM battery, it was an ordinary starting battery. Automotive starting batteries have evolved for a hundred years and the current batteries are excellent for their intended purpose: Start the engine and then immediately recharge, but also built to be cost competitive. They are not happy being discharged even half way, while this is apparently working, it shortens the life of the battery and reduces its capacity. I suspect our usage with the fridge had affected our battery leading to this situation.
This prompted me to work on a better solution. I considered replacing the battery with a "deep cycle" one which is happier about being discharged. Instead, to be better prepared for the isolated boondocking we like to do I decided to add an auxiliary battery specifically to run the refrigerator, leaving the primary battery to its intended purpose, starting and running the car. I also replaced the car main battery to start with a fresh reliable power source.
The auxiliary battery is contained in a box and will only be put in the car when the fridge is there. At other times the box will be stored in my shed with the fridge, connected to a battery maintainer to keep it at optimum charge. I considered trying to mount the auxiliary battery in the car, but there is no good place to put it, and it really is not needed unless the fridge is there.
I started by purchasing an Optima Deep Cycle marine battery, model D34M. I built up a box system using a box I had left over from a previous project, two power point sockets, a circuit breaker, switch, and a volt meter. It also has a 50 amp connector with #6 wire to connect it to the car.
![0811170836-1328x747[1].webp](http://campinnforum.com/community/attachments/0811170836-1328x747-1-webp.2970/ "0811170836-1328x747[1].webp")
Here is the wiring inside the box. I added a block of wood to keep the battery in place, plus it provides a place to keep the documentation for all the parts.
![0811170834-747x1328[1].webp](http://campinnforum.com/community/attachments/0811170834-747x1328-1-webp.2971/ "0811170834-747x1328[1].webp")
Under the hood I added a battery isolator and a 50 Amp circuit breaker. The isolator is a Battery Doctor unit that keeps the two batteries disconnected when the car is not running, charges the auxiliary battery when it is running, plus includes a function that allows a "jump start" feature allowing the auxiliary battery to be connected to start the car if the main battery is too weak for the job.
![0811170832-1328x747[1].webp](http://campinnforum.com/community/attachments/0811170832-1328x747-1-webp.2974/ "0811170832-1328x747[1].webp")
I then ran a #6 cable from the circuit breaker under the hood to the rear cargo area of the car, with a 50 Amp connector matching the one on the battery box. When we are ready to go, the auxiliary battery box goes in the back with the fridge, plugs into the car 50Amp connector to keep it charged, and the fridge plugs into one of the sockets on the box. There is a second power point for other stuff, such as charging a phone or whatever is needed. Also, a solar panel setup could be plugged in here to keep it charged. The voltmeter keeps track of the state of charge.
![0811170825-747x1328[1].webp](http://campinnforum.com/community/attachments/0811170825-747x1328-1-webp.2972/ "0811170825-747x1328[1].webp")
For about $350 I now have peace of mind that we can keep our food supply fresh and be confident we can start the car when we are ready to move on.
This prompted me to work on a better solution. I considered replacing the battery with a "deep cycle" one which is happier about being discharged. Instead, to be better prepared for the isolated boondocking we like to do I decided to add an auxiliary battery specifically to run the refrigerator, leaving the primary battery to its intended purpose, starting and running the car. I also replaced the car main battery to start with a fresh reliable power source.
The auxiliary battery is contained in a box and will only be put in the car when the fridge is there. At other times the box will be stored in my shed with the fridge, connected to a battery maintainer to keep it at optimum charge. I considered trying to mount the auxiliary battery in the car, but there is no good place to put it, and it really is not needed unless the fridge is there.
I started by purchasing an Optima Deep Cycle marine battery, model D34M. I built up a box system using a box I had left over from a previous project, two power point sockets, a circuit breaker, switch, and a volt meter. It also has a 50 amp connector with #6 wire to connect it to the car.
Here is the wiring inside the box. I added a block of wood to keep the battery in place, plus it provides a place to keep the documentation for all the parts.
Under the hood I added a battery isolator and a 50 Amp circuit breaker. The isolator is a Battery Doctor unit that keeps the two batteries disconnected when the car is not running, charges the auxiliary battery when it is running, plus includes a function that allows a "jump start" feature allowing the auxiliary battery to be connected to start the car if the main battery is too weak for the job.
I then ran a #6 cable from the circuit breaker under the hood to the rear cargo area of the car, with a 50 Amp connector matching the one on the battery box. When we are ready to go, the auxiliary battery box goes in the back with the fridge, plugs into the car 50Amp connector to keep it charged, and the fridge plugs into one of the sockets on the box. There is a second power point for other stuff, such as charging a phone or whatever is needed. Also, a solar panel setup could be plugged in here to keep it charged. The voltmeter keeps track of the state of charge.
For about $350 I now have peace of mind that we can keep our food supply fresh and be confident we can start the car when we are ready to move on.
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