I installed a new battery in my First Alert smoke alarm model SA302 . Very shortly after that I smelled electrical insulation burning. I removed the battery and the alarm. The smells as if it is burnt up. What would cause this? Note the alarm beeped once when I inserted the battery. I also checked the battery and it tested good. The alarm has the date 2010 April 20 stamped on it. What would you suggest I do with the alarm? How long do they last?