Ok, the first sign is that the bike won't start....
But most literature on the Odyssey batteries claim a life of up to 10 years.
I've been running these batteries for about 10 years, but have replaced in a "proactive maintenance" mode prior to a long trip, just to avoid the potential for a problem. Usual point in time is 5-6 years.
While I've been told that these batteries do not need to be on a tender, in the winter months I typically rotate my tender between my three bikes.
Recently, I rode in 30 degree temps on my airhead (with Omega charging system), running the Saeng driving lights and heated jacket. I was going to an event where you had to start and stop the bike frequently, and it got to the point of the dreaded click, click, click of the solenoid. A month later, everything seems fine.
Changing the battery on an oilhead 1150 GS is a pain, you have to remove the tank. I happen to have the tank off, the battery is 6 years old, so I just ordered another, even though my LED battery "checker" read good.
Thanks for any advice.