2015 CLS no power at all

[Voguely]

Hi all, having an issue with my 2015 CLS SB. Last used yesterday and was fine. Today no power AT ALL. Had battery on trickle for a few hours now, and still nothing which makes me think it isn't a battery issue as usually you'd at least have electrics working after that time. Currently having to unlock using little manual key. Nothing happens at all on turning ignition and no interior lights etc.

Anyone got any idea how to start fault-finding the cause or experienced this themselves before?

[mk1coopers]

Has it got 1 battery or does it have 2 (one in the boot), if it has 2 have you checked both of them ?