If it was the alternator then it wouldn't stay running, the fact that you can start it off a jump and it stays running means it's the battery, the alternator has nothing to do with starting the car, that's all battery, the alternator then kicks in once the cars is start to keep the battery charged while the vehicle is running. Hope I helped

How old is the battery? You needed to run the car for at least 20 minutes.

And hold the rpm up a bit for at least 5 minutes. And not run the lights, radio, etc.

The average car battery lasts about four years, so you may need to replace it. Besides, I think you need to let the car run for about 30 minutes after the jump.

http://auto.howstuffworks.com/under-the-...

may be a dead cell in battery

you need to let it run for about 30 minutes or longer to charge up.

and i would have the battery tested

I left my car for about two weeks and when I returned the battery was dead. I got a friend to jump it and the car ran and turned on and we left it running for a few minutes before we turned it off. We turned it on again but it was completely dead. Nothing worked.

My friend thinks it may be the alternator but I am not sure. Before I left it there were no symptoms of alternator problems. No lights came on my dashboard. Not sure what to think here.