bought 1999 c240 etstate petrol. sometimes it would not start.battery seemed flat so changed battery. started ok then stalled and would not start. started ok next day. few days later stalled again and battery seems flat? do you think it's anything other than the altinater?

 

1. Auxiliary drivebelt worn or incorrectly adjusted.
2. Alternator not charging at correct output.
3. Alternator or voltage regulator faulty.
4. Short-circuit causing continual battery drain.