Battery light on dash has come on

Help!!
A few weeks ago my battery light came on my dash I took my car to the garage I use he tested it all and said the alternator was ok and battery was getting a full charge but then the other day car would not start so he replaced the alternator so I though yippee it fixed (after a few days of wAlking to work in the rain)Driving it home for the garage and my battery light has come on again can anyone advise on what else it could be please

Check the earth cable from the battery to the chassis.

Mine came on the other night driving home and it was a lose earth connection at the battery - the clamp didnt appear to tighten enough

will have a look and see
thank you

And do try to post just one place theres a good chap.