Help; I have a deepcycle battery thats just off warranty .The problem is if I charge it up say Saturday it goes to a full charge, stays for three days or so and then goes down to half charge and stays. My question is there any thing I can do to revitalize it. Or do I throw the (d**n) thing away .I haven't used it too much just occasionaly for an electric trolling motor when needed. Thanks Plmbr