12volt led van lights dimming

Is it from when your fridge cycles on / off?

Ditto, mine do it also, especially when the voltage gets down a bit.
Regards Philip A

Some of my LEDs flicker a lot, is that the same thing?

Probably the voltage. Put a multi meter on it and watch when the lights dim and when they are bright. It's probably your charger cycling on or off if it's when you are plugged in to 240 volt power.

Sounds like there is something cycling on the system. Keep an eye on the battery charger cycling on and off (you pick this by the system voltage rising above 13 V.) Apart from a compressor fridge do you have anything else like a DC water heater for the sink?