Keyfob battery?

I've had the same battery in my keyfob for three years. It might be psychological, but I feel like i have to hold the remote a little longer to get the security system off.

I decided to buy a new battery. Put it in and it doesn't work at all. Put the old battery back in and it works. New battery back in... Doesn't work.

Decide the new battery must be bad... Hook it up to a voltmeter, and I'm getting 12.5 volts so it's spot on.

Anyone know any business with these remotes and what could be going on here??? I feel like an idiot.