I know that this question has probably been asked before but I need help. I need advice on a durable and reliable deep cycle battery for my boat. I've been through two Interstate series 27 batteries in the last two years. I've always had good luck with Interstate batteries before but now my confidence in them is pretty low. At first I thought it was my charger that was at fault but I've learned that wasn't it. The Interstate battery will charge up to 100% but 30 minutes after taking the charger off it dropped drastically. I am going 3 years on my two Wal-mart trolling motor batteries with no problems. A little help please. Thanks...

Tim