Smoke detector chirping insanity [View all]

Last night we had a power outage. And one of the smoke detectors (we have eight - three downstairs and five upstairs) began to chirp. "We'll sort it when the power is back on/in the morning/whatever" and we went to bed.

This morning it was still chirping. Mounted the stepstool and pushed the test/reset button. Still chirping.

Changed the battery. Still chirping.

Read the instructions. Consulted the Intertoobs.

Cleaned it out with canned air. Still chirping.

Tried a different battery. Still chirping.

Disconnected and reconnected the unit. Still chirping.

Tried yet another battery. Stopped chirping. For a few moments. Then...

Another one of the upstairs smoke detectors began chirping.

And then the one that was originally chirping joined in.

Changed the battery on the newly-chirping one. Still chirping.

Used the canned air. Still chirping.

Tried yet another battery. Still chirping.

Disconnected and reconnected it. Still chirping.

Tried yet another battery. Still chirping.

They're both still chirping, on the once-per-minute schedule that the manufacturer's instructions claim means "depleted battery" but the batteries we were using are Duracell 9-volts purchased at Costco in September of this year and they claim they're good in storage for five years.

They're still chirping... One and then the other. Pause. Chirp... chirp...

I've exhausted my ingenuity.

Suggestions?

Anyone??

wearily,
Bright