electrical/starting issue, insight needed

[MosportGreen66]

Hey Guys,

If the mods want to delete this because its not musclecar-specific, no problem... You guys know mechanics better than I do. I'm just seeking out help.

My BMW is having an electric/starting issue. Its an '85 528e with 62,000 miles in really nice original, unabused shape. The problem started Wednesday. It started fine but needed a jump start after being driven roughly 3 miles and parked for 20 minutes. Later in the afternoon, it needed another jump after being driven a mile and parked for 5 minutes. On Friday, after sitting for 2 days it started up fine. Tonight I took the car out in the rain and it started up fine after sitting all night no issue. Then after driving for about 15-20 minutes max, I parked the car, finish my errand come back to drive home and she won't start. I had to have the car jumped again.

First I thought the issue was the battery but after charging the unit, I know its the root of the problem. It is also an 8 month old Optima Battery. Maybe the battery is contributing, but I have a feeling it’s not the sole problem.

I took the car to Pep Boy's (Auto chain store) and had them test the alternator. The test came back fine and there were no abnormalities found.

Now I am thinking that the issue is the voltage regulator. This whole issue has never happened before...

Any insight would be most appreciated... what mechanical issue do you think it causing the problem?

Thanks.
-Dan