Smoke alarm won't stop beeping?

We just recently installed a new light fixture in our house, and we had to turn off a breaker to do it... unfortunately, it was the same breaker as the smoke alarms, and now they're all going haywire. I have two Kidde KN-COSM-IB combo smoke/carbon monoxide detectors that are three years old. At first they were just beeping every minute or so, so I tried to reset them by turning the power back off and taking out the batteries for a few minutes, but now they're beeping and saying "low battery." So I replaced all the batteries. Still beeping every 20 seconds telling me the batteries are low. Any idea how to get this to stop? Otherwise I'm going to disconnect them and remove the batteries so my ears stop ringing!