Best option for upgrading inverter?

[jdaniel]

My coach has a Heart inverter and seperate charger (yes it cooks the batteries). I would like to upgrade to a newer inverter that includes a better charging system. I have used a Freedom Marine 25 in the past and liked it. I'm sure the batteries would last longer.
My present inverter has a seperate remote panel and it doesn't matter if it's in the on, off or slow charge position, the inverter is still on. My lights, tv and microwave are on the line that I know of....maybe more. Thats all I need to run.
My coach came with 4 8-D but I have added two more. STILL when it sits unplugged overnight, I have to use the merge switch to crank it. If it sits a couple of days it's all too dead. That just doesn't seem right. Am I missing something or would an inverter update be a good idea?
If so, how complicated is it to wire in the newer style inverters?