Just changed mine for the first time, that's 4 1/2 almost 5 years. I've noticed lately that I had to be right beside my bike in order to arm or disarm the security system. Super easy to change, open up the fob, pop in a new battery and close it up...Done.
i guess i'm the odd man out on this one. if the battery goes out on my fob, i will just use the manual disarm procedure until i can get to walmart/dollar store/etc.... to buy a new one. why stick a battery in your tour pak where it is subjected to hot/cold temperature fluctuations that reduce its shelf life so that when you need to replace it, it is only gonna last you 6 months?
The first thing you should do is look at the battery get the number buy a spare and put it on your bike. I keep a spare in my tour pack.
Good insurance, but keep in mind the battery has a 'shelf life' whether they're used or not. So, if you've carted a spare around for a couple of years, you'll want to replace that one too.