by Alain Hoffmann
Dual batteries or high-output alternators? - part 2
The addition of a second battery may sound logical at first. You have several choices for wiring it up. The most basic is by connecting both positive terminals (+ to +) together. This almost adds the 2 capacities together. The disadvantage is that you need 2 identical batteries of the same age. But not 2 batteries are identical in fact and the weaker one always pulls the stronger one down. So after a while you may have 2 dead batteries.
Another possibility is using a 2- or 3-way manual switch. Those allow the charging/use of one or another battery or both at the same time.
Better is the use of an electronic device called an battery isolator. This cares for the automatic disconnection of one battery as soon as the engine switches off. That leaves you always an full battery to restart with. The second battery is ideally an deep-cycle type. Modern kits like the one below by Painless Wiring care for this.
Batteries do not like at all this treatment. Some cope with it better than others however. Optima batteries offer some ddep-cycle types but other manufacturers make them too.
Another solution is to use an high output alternator. Land Rover has them up to around 120 Amps but at an horrible price. Some aftermarket manufacturers also offer HO-alternators. But they all have their price too.
So what to mount if I use an electric winch? I would go with an dual battery setup AND an High-Output alternator as well as an electronic switch.