2017 electrical issues

[Per7y]

Hi folks, newby here and my Van's got some issues. I've got a 2017 trend and when i got the van brand new the battery kept draining and then the van failed to start, after numerous trips and courtesy Van's they said they fixed it and until now it seems to have been ok. The problem now is if the radio is on hour mode it switches off within minutes, and I've used a multi meter to check the voltages, when the van is running it's around 14.2 volts, but when you switch it off the battery drops pretty quickly to 11.3 volts and that's when the radio shuts off. The garage phoned and said the when the van was in when it was new it with the original draining issue they programmed an eco mode thing into the van to save the battery to stop it from draining and they they got very upset when I said their original fix to the original issue has been to hide the issue by fitting a bigger battery and programming it to shut down if the battery gets too low and now its giving issues again. When I told them I just want my van to work the way it should with the radio etc that they'd have to replace the bcm, so to me it sounds like the bcm is at fault and they are trying to hide the issue to save replacing it. Is there anyone who has had a similar issue? I've read about the bcm not shutting down or the sync system not shutting down also. Just need to have some info to battle the dealer.

Thanks