hi ive recently purched a 07 crd patrol its got dual battery system and i work away 4 weeks at a time and was wondering how often i should get someone to start it and for how long to keep them in good working order?
So long as nothing is drawing power from the battieries while you are away, it should be alright just to sit without starting. If you are worried about something drawing the batteries down, either remove the positive terminal when you are going away, or if your Patrol is stored in a shed with power close by, buy a cheap battery maintenance charger and plug it onto the battery while your away.
A 'smart charger' like the Projector series or CTEK should work great with your type of use. After x number of days charging and reconditioning yours batteries it goes into a float charge to keep them topped up - plus on the ctek ones after 21 dats or so it will vary the output to 'work' the battery to keep it at 100%.