I'm pretty satisfied the battery is good, since its been replaced for a new on and failed to start after its first night, plus we've swapped the battery before without success.

I'm not sure what the camera option will do tbh. I think they are hoping the will see if he sat nav is coming on etc, I'm not convinced but what choice do I have. My understanding is they have got the readings from the battery to say its good. If I do disconnect the battery overnight, will it remain alarmed, or is there a chance that the immobiliser could go off, or worse still need resetting etc ?

Its going in after Easter so I will start pulling fuses, do you think if I pulled out everyone that's not important (leaving things like alarm etc) to see if the fault goes away then re-introduce each until the fault returns is the best way to go ?

Another option I thought about was fitting a battery isolator ? Would this work, or would it shut down the alarms/codes etc when not active overnight