Waeco CR110 fridge problem

Hi there,
Hoping some of you knowledgeable people can help me with troubleshooting a problem with our Waeco CR110 upright fridge as I have somewhat limited experience with this type of thing.
Symptoms are as follows.
It works fine on 240v 100% of the time. Unplug from 240v, and after approximately 12 to 15 hours the fridge starts flashing 1 red light every few seconds which indicates a voltage drop issue. This occurs no matter what the outside temperature is or time of day. Could be 32 degrees outside or 20 degrees or overnight it does not seem to matter.
When we are not on mains power we have 300watts of solar on the roof of the van feeding 2 x105amp Fullriver AGM batteries. Fridge connected from batteries with what’s looks to be around 4-6mm wire running approx 2 metres to the back of the fridge.
When the light first appeared the solar regulator stated 12.6v of battery power remaining which was confirmed when I tested the batteries with my multimeter. So I’m assuming availability of power is not the issue.
When the red light flashes, the fridge fan runs for approximately one minute and then the compressor starts up for around 7 seconds, then shuts off, with the fan kicking back in. This cycle then seems to continue.
Now something that I really don’t get. This morning, the solar regulator was showing 12.2v when the compressor was working (again for approx. 7 seconds) and NO red light. As soon as the compressor stopped, the fan started (for approx one minute again) the regulator showed 12.6v, and the red light STARTS flashing 1 time again. Again, all these readings confirmed with my multimeter.
So Im trying to figure out if it really is a voltage drop problem (wiring to small), weak battery problem, thermostat problem, fan problem or something else. Again as stated before, I have limited knowledge in this area. Might be time to pay through the nose for a Waeco repairer.
Any ideas?
Thanks in advance for your replies.
Gazza