Many overlanders add a Dual-Battery system to their truck. One battery primarily as a starting battery and the other to run all of the additional accessories, (Fridge, Lights, Inverters etc). To maintain this dual-battery setup it is advised to install some method of combining/disconnecting the two batteries. When the truck is off, the two batteries disconnect to avoid running down your starting battery. When the truck is running the batteries combine so you can charge your secondary battery off the alternator.
There are many different methods to accomplish this. Personally we went with a Blue Sea ACR
with manual override switch. This system automatically combines/disconnects the batteries when needed while also providing a manual cut-over option in case of an automatic system failure.
You can read my post on the dual-battery setup and wiring. So far it has worked great. I have noticed an issue that if my primary battery is completely dead then I cannot use the Electronic cutover switch and must manually cutover the batteries using the hard switch on the ACR. This may be due to a wiring issue, not sure. Either way, it works and has saved my ass twice. Read more reviews here…