tyres and batterys

Sounds like your batteries weren't charging for some reason. Using the aircon a lot, lights ? I've done this a few times, and am considering a voltmeter on both batteries. Batteries are very misunderstood critters. Starting sucks the life out of em and it takes a while for them to recover. Short trips don't help.
Tyres? I've always said that the most expensive tyres are just a pile of junk if you're unlucky. Better to have some decent el cheapos or a LT tyre if you're swanning around. The big aggressive expensive ones look great and work well until......
I bought some Kellys 2 years ago for an economy price. I thought if they lasted 20Km off the tar then so be it. They are still on the vehicle and going strong after 70000K. Would I buy them again ? You bet. Thats not to say that there aren't better tyres, but thats my experience.

As I mentioned in another post, this is one of the dangers in having two batteries connected together in either an uncontrolled parallel configuration, or "controlled" with a simple (cheap) isolator.

In this method of connection nothing exists to identify that the primary battery is flat, or damaged and the second battery will take over until that too is flat or damaged. Just imagine the possible result if you were in a remote area.

Any good quality isolator (no brands mentioned) should have the "smarts" included in its circuitry to stop this from occuring.

G'day Davoe
Bad luck mate. I haven't had the 2 dead batteries drama but I certainly know what it's like to wreck 2 new tyres in one trip. Ouch.
Which rag tyres do you recommend?

Sand Man - I only use a "cheap" heavy duty solenoid as an isolator, however I have added in a switch so that it is off until after I start the vehicle. That way the aux battery is saved for what it's intended for. Being a deep cycle I've found that if I use it in the starting process most of it's power is robbed and it runs the fridge and lights for a much shorter time before going "flat". And it simply doesn't charge back up properly from the vehicle.