Adding a second battery does two things...
1. It allows you to run your extra van electronics longer and...
2. It ensures that your starting battery will have enough juice to get you going in the morning.
I have always had 2 batteries in my van but one of them was a jumpstart battery pack that I only used to power a small fan in the summer. I had a 12v solar panel to charge it and I would put it out during the day to charge. The battery pack worked but when I added the Edgestar fridge I quickly realized that I needed a second, high capacity battery to run it and a way to charge that battery.
I settled on a type 27 marine battery from Advance Auto Parts. I bought it and a plastic battery box and some heavy gauge hookup wire. I also ordered a battery isolating solenoid from Amazon.com.
I built a small tray inside the cabin of the van and although this is not the best place for the battery, it was all that was available. There was just no room under the hood. The battery box is vented since most batteries produce hydrogen gas (very explosive!!) when charging. My van is a conversion van and the interior lights, radio and CB run from a dedicated fuse box inside the van. There was a cable attached to the starting battery for this fuse box and instead of running a new wire I simply attached the existing cable to the house battery side of the solenoid....
Yes the SOLENOID. This is a very simple relay that makes a connection when 12v is applied to a terminal. Hooking the solenoid up is very easy. Mine grounds to the vehicle so I found a spot near my starting battery, scraped the paint away and screwed the solenoid in with self-tapping screws. On one of the main posts of the solenoid I added a heavy gauge battery cable to the positive terminal on my starting battery. On the other post of the solenoid I ran an 8 gauge cable to the positive terminal on my house battery. I grounded the house battery to the body and my second battery was almost ready to go. The solenoid needs to be turned on/off by the ignition. Under the hood of my van was a connector (for something) that was not hooked up. It had 6 connections and with a little trial and error I was able to find a connection that provided 12v when the ignition was turned. I ran a wire from this to the small post on the isolator and made sure it worked by listening for the solenoid to click when I turned the key on.
When I turn the van on the solenoid closes and connects the second battery to the first (and the alternator). When I turn the key off the second battery is isolated from the starting battery....simple right???
I also hooked up my solar charger to the second battery with a charge controller. The solar charger cuts in when the battery is low and turns off when the battery is fully charged. The charge controller is super simple and I mounted the solar panel on the roof and bought an extra long cable to hook it up.
From my second battery (house battery) I am running my fridge, a 3 way 12v plug for my cell charger and any extras, a 12v fan mounted over the drivers seat, another fan that clips on near the bed, my pump for my sink, and a 12v hand vacuum when needed.
Everything is also fused. I have a large fuse on the wire running from the solenoid to the second battery, a fuse between the second battery and the fridge, between the second battery and the pump, the interior lights are on a dedicated fuse panel and the fans both have fuses built into the 12v plugs. Everything should always be fused.
Here are a few things that I learned during my install...in no order whatsoever.
if you are running a cable through sheet metal, use some cable protection through the hole like a rubber grommet (this was a 200$)
make sure your grounds are good
use the heaviest cables you can afford and nothing less than 10 gauge
draw everything out on paper first
cable management is very important especially under the hood
label your cables
use the proper connections on the end of cables
don't electrocute yourself
disconnect both batteries while working on the system
learn how to reset the clock on your radio
That's it for now.....