any ideas??
 

I have a 1988 300E car started fine this morning in garage she drives 15 miles stops for about 5 minutes at a store then calls me car will not start I get there and battery appears to be low? light come on but dim when I try starter..... jump car and it starts ok drive home about 15 miles and car starts ok now? and appears ok as she has used it now 3 or 4 more times and it starts all the time now so appears its charging ok? any ideas on this? Thanks

This sounds like an alternator that is coming and going. I would check and replace it soon.

I had something like this with my '91 Lexus LS400. Then one day it didn't start at all. Couldn't jump start it either. Ended up replacing the battery terminal clamps since corrosion had been deteriorating the old and put in a new battery. Not only did it fix the starting, it also seemed to perk up the electrics over all. I'd check the terminal clamps and pull the battery and have it tested.

How old is the battery? Have it load-tested to see if it is any good.

I had similar happened to me about 2 months ago and it turned out to be a bad battery (won't taking charge). Initially I thought it was the alternator/voltage regulator.