Yes its for a caravan/trailer.So all of it can be wired in from the boot.What is a split charger
It's a relay that connects your car battery & caravan battery together to charge it on the move. However, you only want them connected when your engine is running, so you either energise it from a take off from the alternator, or, the usual way to do it these days is to use a Smartcom(??) relay. Electrickery in it can sense whether your engine is runnning by the voltage at it, and so switches only when your engine is running. Its advantage is, you don't need to drag a cable the length of your car. Be aware though that later caravans are wired slightly different from older vans ....... can't remember differences though. :-/ Google will know though.

It's also for your caravan fridge. You only want your fridge trying to draw current when your engine is running ... 8-10amps rings a bell ..... so would flatten your car battery in no time if they were directly connected.