Help! Car won't start after trying to replace power window button.

[LJR]

Thanks. Sometimes the battery light is lit up when I start the car but I have not noticed it lit while driving. At first the AA guy tried to sell me a new battery. Then he tested the alternator and stopped trying to sell me a battery and just said that the alternator needs replacing. So even though he tested both the battery and the alternator you think I should just get a new battery first?

Can it be that the reason the alternator is not charging the battery sufficiently is because the battery isn't good?

I left the car at the garage this evening with the key. Should I call them tomorrow and ask them to replace the battery first and see what happens?

Thanks for your help.