Charging of batteries can be done via 12v from the vehicle alternator when the engine is running, or 240v EHU when plugged into the mains. You can decide how to have your installation done, it’s usually preferable to have both options.
12v charging was always historically done via a split charge relay. A split charge relay is a unit which allows your alternator to charge your leisure battery when your vehicle is running and stop charging when your vehicle is not running. This system is great for topping up your leisure battery however, depending upon vehicle usage and alternator output, it can be a primitive way of charging an additional leisure battery. On newer VW transporter models from the T6s onward, the vehicles come equipped with a smart alternator. These clever units are designed for optimum fuel efficiency and do not provide the same charging rates as older alternators. On modern vehicles it is important to use a charge system which is suitable for a smart alternator. This can be done in a number of ways, but Exploria have found using a battery to battery charger to be the most effective and robust.
Even with the right 12v charging system for the vehicle, output from the alternator is often low and variable. For safety reasons and to ensure trouble free operation, it is very important that the fusing and wiring is capable of carrying loads to and from the vehicle battery. As good practice we use high amp components, 4 gauge cable or higher, along with correct fuse types and sizes.
240v charging can be done in a couple of ways:
- An in-built vehicle charging system
- A stand alone battery charger. This requires a quick coupling to your leisure battery or easy access to the terminals to allow charging. This is the cheapest way of being able to charge an additional leisure battery, but is not that practical for regular use.
Charging by 240v is the best way to charge your leisure battery. This is because the charge is normally at a consistent rate and is a much higher amp than possible from a standard vehicle alternator. You have to bear in mind that it can take up to 15 hours to fully charge a 100amp leisure battery via a 12v charging system running from the vehicle's engine. Alternators don’t have this amount of surplus; consistent power and a 15 hour journey is not generally practical every time you wish to charge your leisure battery!