Deep Cycle Starting or just Deep Cycle

NEVER mix battery ages when they are used together. You need to replace BOTH at the same time and keep the better one for an emergency. Even Interstate replaces all batteries in a battery bank when one fails under warranty. DEEP CYCLE SRM batteries are the STANDARD preferred choice for RV Coach systems. AGM batteries are used when the RV'er does NOT want to check water levels and wants to avoid outgassing and corrosion from wet cell batteries. But, as you found out, you pay a lot more for that convenience. You NEVER install a Deep Cycle SRM type battery on a chassis starting system. You always use a chassis designed battery. Doug