Join Date: Mar 2008
Location: Hamilton, ON, Canada
I don't have a Battery Tender, and my bike and its battery is now almost 6 years old, and still works just fine. Typically my bike only ever sits for long periods (2 months or more) without running in the winter. If it's an especially bad winter, after a couple of months I will throw the trickle charger on it overnight. Self-discharge is slower at lower temperatures, faster as it gets warmer. Even so, a couple of weeks of being parked in my hot garage in the summer has failed to ever drain my bike's battery.
So, it can't hurt to use a smart charger, but they're not strictly necessary in my opinion, and experience.