I'll ask here .... better chance of a reply rather than the MB's forum standard reply of take it to a dealer/indie.
If I wanted to use a CTek on my ML due to it standing more than normal, does anyone know if the auxiliary battery in the 'boot' get charged if I just connect the charger to the jumper connections under the bonnet? (starter battery lives under the driver's seat) Access to the aux battery requires dismantling of the boot liner/carpet.
I'm not really sure what the aux battery is for .... some suggest it's something to do with stop/start.
The small battery *should* be OK, but getting a bit of charge in it if its not being used wont harm at all. Long term deep discharge will damage it still.
Main battery, given that the Ctek is at the best of times a woeful piece of shit, get it as near to the battery as possible, though taking the hhydrogen/spark issue seriously. Additionally, it must be the other side of any battery monitoring system that modern cars have, so the monitor can see the electrical pixies going in, as well as going out.