Solar panel to leisure and then engine battery

Hi all,
I have a nice solar panel on the top of my van feeding the leisure battery, but my engine batteries died after I didn;t drive the van for 3 weeks or so. Am thinking of running a feed to the engine battery...I am assuming it is a fairly easy job...where do the wires run from - there is only one battery terminal on the solar control unit, so do they run from the + and - terminals on the leisure to another voltage regulator and then to engine battery?
Thanks in advance

You'll be needing one of these then:

https://www.amazon.co.uk/battery-controller-regulator-motorhome-batteries/dp/B006OA8LKQ

GPW wrote:

You'll be needing one of these then:

https://www.amazon.co.uk/battery-controller-regulator-motorhome-batteries/dp/B006OA8LKQ

Simple when you know how

Alternatively use a voltage sensing relay between the batteries that works in both directions.

I use the Cyrix one, so when the engine is running it charges the leisure batteries, and when on hookup (or when my solar panel finally arrives!) it will charge the vehicle battery as well.

It also allows jumpstarting from the leisure battery, but you will need hefty cables for that.

http://www.12voltplanet.co.uk/victron-cyrix-ct-voltage-sensitive-relay-battery-combiner-1224v-120a.html

Thanks chaps, think I am gonna go for the dual controller