If you have a euro 6 emmisions vehicle you can't use a standard split charge system, a 'batttery to battery' charger is what you need instead, and this sterling one is great.
These new Battery to Battery chargers from Sterling are proving ever more popular. This device fast charges your batteries as you cruise along without the need for complex wiring, touching your alternator (voiding its warranty) or tampering with the electronic control unit (ECU). It provides the onboard batteries with a fast 4 stage charging profile with very simple and speedy installation. All the benefits of advanced charging without any of the drawbacks. Simply connect the B2B between the battery being charged and the battery you wish to charge. This version charges at the rate of 30A.