Paul

G'day mate I'm assuming that you want to keep them connected while engine is not running, aka you want to use thewm both for cranking or winching for example to utilize the "overide wire".

Good in theory but trouble in practice especially if your Redarc installation has not been done with this in mind. In another words the wiring between batteries is not heavy guage enough as in most cases happens.

So if you don't have minimum 35 mm²  cables between both batteries and Redarc in the middle then you are running serious risk of burning your under sized cabling if it subjected to high amperage loads.

Have a look at the starter motor main battery cable size, if you have the same size connecting both bateries then good use the overide option.

As for the switch, any will do if you use a control relay with it, otherwise use something like Carling switches or their clones

The clones of above unit are available from Narva or Jaycar and you can specify a decal or if it is

monostable (momentary spring loaded return)  bistable (two position on return)

Narva 4WD switches Carling style

Switches

Regards

Thanks for that info.

I just wanted to use 2nd battery for a jump start if needed.

Sound like a good set of heavy duty jumper leads in parallel  will do the trick, as Redarc cable is only 6mm which wont supply enough power.

Cheers mate