Deep Cycle Marine/RV Battery The GPL-31T is a high performance, Mil-Spec, AGM battery, produced in the United States. Due to the Lifeline Battery’s quality construction, it has an industry leading 2% per month self discharge rate at 77°F (25°C), compared to 10%+ for conventional batteries. Coast Guard approved, DOT Haz Mat Exempt, and longer lifespans than conventional batteries. Warrantied installations include marine, yacht, and other seafaring applications.