When I lived in Denver, batteries lasted less long than my previous experience as a California driver. Back in California now, the battery on my 2003 Explorer couldn't even play a music CD for 10 minutes recently. The engine wouldn't start without a jump. Batteries just wear out. I took the old battery down to Batteries+ store in my sidecar moto and replaced it. I'm good to go for our mild SoCal winter and another 5-6 years
I just got a 2009 GZ250 with only 132 miles (now nearly 400). This bike was barely used and probably rarely started during the last 2 years. Yet this small battery is still good to go on "cold" 45-50 F mornings
I expect it will last another 1-3 years.
Fred