Split charge relay, big fuse and a big manual switch. BUT. Unless you really really need it a winch weighs a lot and hardly gets used, and the 2nd battery weights a lot too. Look at the total KGs your are planning to add and where it is as it can mess the road manners up for little benefit. My preference is for a Tirfor. OK hard work (and more..) but you can recover in any direction and you can leave it at home if you are only going to the shops. The problem with all electric winches is that they don't work well underwater, also you may need to run the engine to keep the volts up but that's only possible if you are not about to roll over. Hand winches just work whatever. 800kg Tirfor and a snatch block should do most jobs.