Not sure if you have these over there, but I have an aftermarket dashboard mounted solar panel that plugs into the lighter fitting, which trickle charges the battery during the day. As I am spending more time on the motorbike these days, it's nice to know that it's fully charged and will start when you need it.
I first saw one of these on a Stag in the long term carpark at Sydney Airport 20 years ago and thought what a great idea, and are now quite easy to find in Auto Shops here now for about $50.