my 2003 mini cooper s battery reads 12.9, the alternator 14.7 while running, but still wont start without a jump. whats wrong

 

Good question. You’ve confirmed Voltage is good at rest with no load, but it also takes amperage to turn over a starter. Turn on all the lights, radio, ac, ignition etc amd measure the voltage under load. See if it is dropping significantly?


or take the battery to be load tested to see if it is still good or might have a bad cell or two.

 

+1 for getting the battery tested. If it's consistently starting with a jump it's most likely not the starter.

 

^^^ What they said. Just went through the same thing with my R53 -- 12.9 across the battery, 14+ while running (after charging the battery to 100% and starting once). After that start, back to nada. New battery solved the problem.