Depends on what you are trying to do. If you just want more amps and battery run time, no. Just wire them in parallel. Both batteries would be used all the time. They will charge at the same time and discharge at the same rate. If you want to control when and how you use the second battery, than you need at least a switch. The switch and soleniod will allow you to seperate the batteries when they are not being charged. You would do this in order to have the second battery in reserve in case there was an issue with the first (jump start yourself) or you can run all of your high draw accessories off the second battery without ever effecting the first. It could go dead, but you could still start the truck from the first battery. The process of switching would be manual. You would have to remember to switch it back and forth. The controller adds automation to the process, but can be used in manual mode like the switch. It offers the added bonus of dual voltage gauges along with the switching function.
