UPDATE: my BAHA is working! I tried it again (after trying 4 fresh batteries the first time) and it's working FINE. This has happened to me once before, last year, when I thought i just had 2 dud batteries in a row. It's like it needs a little rest of several hours.
At any rate, I'm so relieved, but I'm still going to schedule an appt. w/the audiologist b/c I think this means it's time to replace it anyway. They're only expected to last 5 years, and mine has been in use 5 years + 10 months.