Most people ask why would you want a dual battery in your rig. Simple answer is the 2nd battery can be used to “jumpstart” the primary battery. It can also be used to power all the always on accessories you have on your rig like my HAM Radio, CB, Fridge, and one of my dual USB ports.
The 2nd Battery is a deep cycle battery. Deep cycle batteries are better suited to power accessories.
I went with the National Luna Battery Manager Kit. It is one of the more popular options. Not the cheapest but has a good track record. When you start the vehicle the system charges only the primary battery for the 1st 5 minutes. It then kicks over and starts to charge the auxiliary battery. No intervention in required on your part. If you attempt to start the car and your main battery is dead a simple press of a button inside your vehicle pairs the batteries. You should then be able to start your engine.
With a huge helping hand from my friend Don Grey the install was a success. Don had to build a custom platform for my purchased battery box. The battery is installed on the passenger side over the wheel well. Since this is not level you have to build something to level the box. Don did a great job. Something I could have never built myself since it required welding and customizing parts. The National Luna install is really easy. Once complete I simply had to build one new positive cable for my fuse block to run to the auxiliary battery. Once again Don saved the day an built one. If you want to purchase custom cables I recommend trying this company. Pricing is very reasonable.
A few pictures for your viewing pleasure.