Speaking of weak battery.
A few days ago, my 87 300TD took two cranks to start at 33 deg F. That was a bit odd as it had always started on first crank.
Looked at the records and found a new MB battery was installed about 1 year ago. It is one of the maintain type that you add water, etc.
So I opened the holes and filled with distilled water. Oh, boy, it took half a gallon to fill all the holes. The liquid must be seriously low. After adding water, I put on the 1.5 A automatic trickle charger (just purchased). It took about 5 hours for it to fully charge and the charger tuned it off automatically.
Now I cannot believe the difference. As soon as I crank, the engine starts. Also there is no smoke after I glow it once. Before, I always see some smoke at startup.
My conclusion is that the weak battery is not running the glow plugs hot enough and not turning the starter faster enough.
I then used the charger on my other two cars. My 300E has one of these maintenance free type battery that has a hydrometer check on it. It was green and the instruction says it should be 50% - 100% charged (a big range). It took 4 hours for the charger to turn off.
The E320 was even lower on charge. After 5 hours the charger is still on so I went to bad and let it charge over night. In the morning, I checked and the charger was turned off.
You may want to use one of these automatic trickle chargers just to make sure it is fully charged.