Redarc dual battery system - strange happenings

First of all, Merry Christmas!

I have a problem with my dual battery setup. I am running a CAT 650CCA battery for the main and a CAT 750CCA for the aux. Using a Redarc 100A controller.

Whats happening is this: I will leave my fridge going all day (draws 3 amps when running), and within 10 hrs the aux. battery is flat. I realise that the battery is probably stuffed and not going the distance it should, but the plot thickens.

Yesterday at work i had the fridge going to keep our bevvys cold for knock off time and within 8hrs it was flat. I drive an hour to work so it has a good charge time. Also my 2way and stereo run off the aux battery. On the way home, fridge off (but full of ice) the stereo cut out on low voltage which means the redarc controller didnt connect the second battery. I went out to the car this morning, the aux battery had 11.5v. I started it and after about a minute, the redarc relay kicked in and the aux batt was being charged.

Why did it work this morning and not yesterday when i needed it too?????

It has done this once before and yes it is wired up correctly.


Thanks and have a good one,

Nath