Components of a Dual Battery System

Components needed for a dual battery system in a 4×4

Let’s do this for a bakkie with the battery in the back of the vehicle and with a full power distribution system. This is how it was done 2 decades back:

Fuse at the 1st battery, then a basic heavy duty relay, and some 16mm square cables to charge the second battery.

Due to the high voltages required to charge modern deep cycle batteries this approach has now fallen by the way side. We now use dc2dc chargers, as follows:

This way we are now SURE the charge voltage is high enough to fully charge the 2nd battery. Since the dc2dc charger limits the charge current we can now use a 4 or a 6mm square wire from the front to the back. Note how the dc2dc charger is located close to the 2nd battery.
But you want to camp without having to run the engine, thus you need to add solar :

With this setup the alternator can charge the battery while you drive. And while camping the solar panel can charge the battery.

If you were to use a Ctek or HcDP dual charger your setup would look like this:

Okay, so your charging circuit is sorted, now let’s look at the distribution from the second battery:

Combine all of this and you may well have a “dual battery system” that looks something like this:

Article by ChrisF