Quote by the fat controller
What’s it for?
An intelligent split charge relay. Charges the leisure batteries better when you are driving as it uses the engine battery, reducing its charge and making the alternator work harder therefore putting more charge into your leisures. Its is also an MPPT solar regulator and it decides which is best to input your batteries.
It charges on a 3 stage charge for a better charge so should prolong the life of leisures.
Alternators are not good at charging leisure batteries, you would need to drive a long long time. The sterling one that @baguette
has I would say is a lot better but its twice the price.