The story so far, because people are getting confused:
Definitely free from west to east:
Tesco garage (London Road)
Sainsbury (London Road)
Abbey (London Road)
Barclays (Dartmouth Road / London Road)
Forest Hill station (x2)
Sainsbury Metro (Stanstead Road)
Post Office (Brockley Rise)
Barclays (Crofton Park)
Sainsburys (Bell Green)
Another possible location of a free machine:
Co-op (Waldram Park Road)