I had a friend who passed awy some time ago that had a boat docked at one of the larger recreation lakes in the state. I remember he had the bilge pump hooked up to a small lawn tractor battery with a trickle charge attached. He would be back home in the off season and never go near it for months and would come back to find the pump doing its job. The battery lasted for a good 5 to 7 years that I knew of. Poor guy had plans to retire but before he could he suffered a massive heart attack and dropped to floor dead. He use to joke he looked forward to alzheimers in his advance years because then there were no old jokes. I guess the grim reaper got the last laugh on that one.