Besides buying a new marine battery, is there anything I can do to revive this battery that seemed to have gradually lost charge over the 2 years that I have owned it. I don't seem to get the same charge out of it as previously. Any suggestions besides shelling out 100 bucks for a new Deep cycle marine battery? It is used with a 30lb Minn Kota trolling motor and that is its sole purpose. thanks in advance!!!