Hey scotty, in my boat (Chevy based engine) both of my batteries completely died to the point were not even my cabin lights would come on. I have a blower (ventilation system) that turns on but it is very weak. proving that it wasn't a electrical short (i think). i have 2 batteries and i hooked up a charger to one of the batteries and let it charge for about 1 hour and 30 mins. nothing happened at all. i have a 30 year old charger for my batteries that Im unsure of how well it works. (it worked fine a couple of weeks ago) do you have any safe ways that i could test my charger? i let my boat sit for 2 weeks and protected it from the weather. is it like batteries to just suddenly die like that? they worked fine a few weeks ago. Im planing on taking both of the batteries to auto zone to have them tested for free. do you think that if i replaced just one battery it would do the trick to support the other battery? quality deep cycle marine batteries cost sometimes well over $100! the batteries are both over 3 years old. i have noticed days before that it droped voltage from around 12 volts to 11ish volts. to sum up, im asking how or why my batteries suddenly just gave up, how to safely test my battery charger. any advice would be helpful. thanks everyone!