Before thinking about replacing batteries, you should get a better battery charging system. Your present single stage charger will kill any battery you choose to replace the Interstates.
Leaving a liquid cell battery unconnected by itself in a dark room will result in a dead battery in about 30 days from the high rate on internal resistance and self-discharge of these types of batteries.
There are far better alternatives available.
RVIA/RVDA Nationally Certified Master Tech
Master Tech Energy Systems, Inc.
AM Solar Certified Installation Center
Lifeline Batteries**Magnum Inverters
Lew Farber...RVIA Certified Master Tech...ABYC Certified Master Marine Electrician
SOLAR TECH ENERGY SYSTEMS, INC.
AM SOLAR ...MAGNUM…VICTRON ENERGY...LITHIUM & LIFELINE BATTERIES…MARINE REFRIGERATION