Sounds like the alternator. Check the connector at the alternator, ensure continuity back to the large starter cable.
I have managed to adjust valves in the past before I bought the wrench set, but you need to make sure you have enough bad words lined up before you start, it's challenging without the wrench set.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in