I bought a very small battery recharging solar panel from Maplins......about a tenner......to top up one of my cars as I only use it for golf & can't play at the moment. It's done a grand job as it has stopped the car alarm from draining the battery & the car started the other day ,after lying unused for 2 weeks and despite this very cold weather. I 've bought a similar one thinking that it may do the same for the starter battery on the boat but haven't fitted it yet. Have to work out how to position it so that it doesn't get "borrowed" when I ain't looking!