@ Harvey
I ride the bike once or twice most weeks, all year round in a fairly mild climate. It's not primary transport, so it never has had daily use - up to about 47,000 kms.
I've had 4 periods of about 2 months each of no riding so I charged the battery up using an Optimate 3 charger before storing it & before riding it again. I don't have it on the Optimate all of the time. I'm replacing it with a new Yuasa after talking to a car/bike battery expert even though they are about $320 down here ! He recommends CTEK chargers, but I know that the Optimate is well regarded in the UK & here.
I don't have any electrical farkles drawing current, so maybe that has helped with it's longevity. If this one lasts as long (& I'm using the bike more frequently now anyway) I'll be stoked.