I've owned my ST1100 for 27 years. The first 15 years I rode practically every day of the year, and my battery lasted about 7 years each. Since then my number of riding days went way down, and battery life went down with it. Now that I've been working out of the house for the last 5 years and rarely ride at all, my last battery lasted around 4 years. My empirical evidence suggests that riding every day and keeping the battery fully charged helps extend its life by a noticeable amount.