Hi guys this is my first post and hoping someone may have some ideas on my issue
08 ml500 for last few weeks the car has taken a while to start and a bit slow in cranking as if it was a dying battery , today it just won’t start at all not even a tick tick as you’d expect from a flat battery .
Ignition turms on , all accessories seem to be wrking but it won’t crank over nothing at all
Tried to jump it with a jump pack and also with another vehicle and jumper leads but still nothing.

Any ideas i’m stumped

Battery is fine all electronics working
I’m thinking possibly a starter motor issue or crank sensor

Thanks that’s what im thinking
I just went to see a European specialist mechanic and he tried telling me it’s going to be the auxiliary battery and located under the hood on a 08 ml500 I tried explaining as far as I know it’s only a backup for the auto trans and he couldn’t even tell me the correct positioning of that battery.
So is there a way to test the starter and should I attempt to replace it myself.

Nothing is easy on this bloody car
I’ve replace front right strut twice , front air compressor , rear tailgate motor , Sam module , the list goes on and it’s only done 95,000 kms

thanks for the pdf & your help.

2008
tried changing it not sure if it has I’m still trying to wrk out the site.

Done thanks