Went to jump in the car the other day and battery was dead. Jumped it this evening and started fine. Drive about 20 miles with no issues. Reversed into a parking space. Put both windows down so I could see properly and when putting them back up together it seemed to be draining a lot of power. Lights went dim. Reved the car ran it for a further 5-10 minutes. Made sure everything was off. Turned the car off. Went to start it again and wouldn't start with symptoms of a flat battery. I had no warning lights or anything previous so I suspect the alternator is fine and guessing its just a duff battery? What's people's opinions?
Cheers