I have one that's quite sensitive. Goes off if bug spray or hair spray is sprayed in the TC or just about any aerosol vapor. Even very small amounts.
I don't remember ever having any voltage issues causing it to alarm. And I have had a low battery a time or two. It does chirp one time when the power is removed. Not sure at what voltage that occurs.
Manufacturers specify a expiration date of 6 or 7 years. Not sure if they get more or less sensitive.
Like DrewE said, disconnect the solar leads and check it with just the batteries.