Mercedes c class 2009 starter motor

[Matt231b]

Hi - Recently my car barely tries to start when you turn the key. It's a bit like the battery is almost flat. But I swapped out the battery for a new one and it is still the same - could it be the starter motor itself, what do you advise please?

[E-bmw]

Firstly borrow a multi meter & check the EXACT voltage on the battery, it should be 12.6 - 12.7 volts if the battery is well charged & has plenty of life left in it, for every 0.1 volts below that it has lost around 15% of its potential charge.

Then put it on charge overnight & check again if it is anything less that 12.3/12.4 volts and test again after putting the headlights on for a couple of mins.

If that is all good then remove, check, clean & refit tightly ALL high power positive & earth cables on the battery, chassis/engine, alternator, starter & main fuse input first.

Then try again, up to this point it will cost you nothing & will rule out most of the most likely problems.