Knackered battery causing errors

I was thinking primarily of reversed polarity with a charger that doesn't detect polarity.

Hi Graeme and if the battery is in place, and the battery charger does not have reverse polarity protection, then you will most likely destroy the battery charger first.

The battery itself, because of it’s size and ability to withstand low current polarity reversal, even if dead flat, will protect the rest of the vehicle’s electronics.

Reversing the battery’s leads is a different thing but reversing a battery charger’s leads would see the battery charger’s leads melt and/or the charger cook itself.

Is there somewhere in Brisbane I can get a connector made up for the trailer power point that connects to my CTEK?

I've got a CTEK lead that can be cannibalised which just has black/red cables on it.

I have used one of the large round trailer plugs and depending on the brand you can rearrange the pins to suit the LR socket with the live to battery connection. If you unscrew the wire retaining screw on the pins you can slide them out and rearrange the pins to suit the required positions in the LR socket.
Perhaps a poor description but it should be obvious if you dismantle a plug.
Regards
Barryp