Hmmm wouldnt do that on a big Mercedes.
They have a seriously extensive dual battery set up. And the Battery control module is very expensive. If you have their dual battery set up, its vital you disconnect and connect in the correct sequence .
Ignore that at your peril !!
Even if you have the single battery set up, like on the later cars, I definitely would avoid trying to set up your own home brew version. E.g. one Tuner Control Module for the HK Amp is £1,390 unfitted!
... as you could blow up even more expensive SAMs. Quite easy to kill off £2,000 worth of control modules
You would also definitely void your warranty.
If in any doubt ask your main dealer’s Electrician.