Dual Battery Setup on an Astro


One of the biggest problems I have had with my Astro conversion van is running the battery down from watching TV ,playing games, or other random messing around in the van. The best solution was to add a second battery to handle the load while the van is off. I wanted an automatic solution that didn’t require me to remember to flip switches or mess with it in any way.

I started by getting a battery isolator from Amazon.It is a pretty simple device and was not as hard to wire up as it looks from the instructions. The factory alternator is either 100 or 105 Amp so the regulator listed here is a good one for the job. I also needed about 25ft of 8 gauge wire and assorted crimp on connectors.

I also picked up a deep cycle marine battery and case from Walmart. On my van there was an old battery powered vacuum cleaner that didn’t work and I had no interest in fixing. I have left it there for the entire time I have owned the van just taking up space. I figured that would be a good spot for the battery to mount. I took the vacuum out and cut the hole out bigger by going straight down from the existing hole. I will make a wooden box and stain it to match the existing wood later to make it look nice.


With the battery mount figured out I had to drill a hole through the floor and run the wire to the front. I just grounded the battery to a hole already in the support panel behind the tail light. I crossed the wire over to the drivers side behind the transmission to keep the wire away from the catalytic converter. The only place I could find to mount the isolator was beIMAG0004side the battery tray. I just had to move one bracket that held the starter wire in position and I was set to mount it. Wiring it is straightforward just follow the directions for the Delcotron CS-D alternators. To find the S wire location look on the back of the alternator and the connections are labeled there. Take the existing charging wire off the alternator and tape it up out of the way good so it doesn’t short out. Run a new charging wire over to the isolator as the instructions show. The original wire runs down to the starter and is inside the harness so it is impossible to use it without a lot of work.

Now that the battery was hooked up and could be charged it was time to move some of the stock circuits over to it. The easiest thing was the add on panel from the conversion company had a separate power line going out to the battery. It had a relay built on the panel so it would come on when the key was in the ‘accessory’ or ‘on’ position. I just had to take that power wire and connect it to the isolator post that went to the second battery. That moved the TV and conversion lights over to the new battery. I also moved the power windows, radio, and dome lights over to the new battery. for the radio, it was easiest to just unbolt the fuse panel and cut the brown wire that feeds the radio and all other accessory circuits. I then attached it to the relay on the addon panel so they would come on when that relay was energized. For the power windows and dome light I pulled the fuse out of the panel and using a couple of crimp on terminals to attach the fuse to the addon fuse panel. I then ran a wire back up to the output side of the fuse using a spade terminal pushed into the old fuse location that went out to the accessory. Now my windows, dome light and radio are on the rear battery as well as all the conversion parts. One really nice thing is the windows now work in the accessory key position, they used to work in the ‘on’ position only.

This setup is now complete and working good in my van. I let it sit and play the radio with the dome light on all day. The only power being used from the main battery was to power a relay and the radio memory. Both of those loads are tiny and would take a month or more to run the main battery down. The van started right up and the alternator started charging the second battery back up and at the same time keeping the main battery voltage at 14.7. The only thing I might add is a switch to turn on the accessories without the key just for convenience. For now it is nice to not have to worry about the battery going dead from extended use of the accessories. With the 115AH deep cycle battery I should be able to run the TV and valence lights for about 8 hours without running the battery down low enough to hurt it.