A range of Voltage Sensitive Relays and Alternator Splitting Diodes.
The VSR relays are designed as a simple and cheaper fix for charging a secondary battery from your primary starting battery. You simply connect the positive from your primary battery to the relay and then link to your secondary leisure battery. The VSR is pre-programmed to switch on and off at certain voltages when the engine is running and the alternator is charging.
Please be aware than these relays are not suitable for vehicles with smart alternators (euro 5/6). If your vehicle has a smart alternator then we recommend you take a look at the battery to battery charger range.
Split charging diodes are the best choice when safety is of most importance as they stop any back feed going through the diodes, thus ensuring that high currents from other battery banks do not flow up the charge lines and cause a fire. However they have a higher voltage drop than a voltage sensitive relay. This can be rectified when used in conjunction with an alternator regulator to boost the voltage.