I have a 1992 5.7L Mercruiser on a 24" Rinker. One of my batteries has a leak and the other is almost 10 years old (although seems to hold a charge fine). I'm thinking its time to replace both. I've read a bit about having a starting battery and a deep cycle one (I have a switch). What else to do need to consider? How do I determine what size to buy? Does anyone have recommendations on brands to buy or to avoid?