The vehicle will not start on the first attempt, or takes a few seconds. If the car has been driven for over 30 min - 1 hour, it will start up just fine. Leaving the car off for over an hour will cause the issue to arise again. Freezing temperature does not seem to play a factor. Battery voltage shows 11.9 V when engine is off. Will be replacing battery either way, but could this be the cause of the issue? Its a 2011 ML350 Bluetec (Diesel)

Thanks in advance

 

The engine needs a certain cranking speed achieved quickly to build fuel pressure on the high-pressure side. Could for sure be a weak battery. In my case a weak starter was a big part of the problem. Also be sure your air filters are in good condition, you don't have any small fuel leaks, and fuel filter is good.

If your engine is operating on the low end of the starting threshold like mine was, it will start eventually but will usually take quite a few cranks. But sometimes it will start quickly which can make it harder to nail down.

Maybe have the battery tested before replacement, then go from there.