I like to read all the electrical threads. I was an apprentice electrician back in the 70's, and switched to a telephone job for a carreer. I've had some training and I have a little apptitude. Having said that, inverters/converters/chargers can be mysterious. In my 4 years of motorhome ownership (2001 Apline Coach), I have had a couple of problems that I thought were inverter issues, and they turned out to be something else. Reading some of your posts make me believe that you have some of the same misconceptions about how things work that I had. I'm going to share some of the fundementals I have learned with the caveat that your coach may be different.
I have an inverter/charger. Some people have inverters/converter/chargers.
Since I have an inverter/charger, all 12v power comes from the batteries.
My inverter/charger will only charge the house batteries unless there is another piece of equipment to sense when the house batteries are fully charged, and transfer the charge to the chassis batteries. On my coach, an Echo Charger performs this function.
The path of power through the coach is more complex than I expected. It was a while before I understood the reason for 2 panels. I also have some 12v items (steps, refrigerator, 12v fuse panel) wired directly to the batteries. I made a diagram that helps me keep this straight in my mind.
On shore power, power comes through the transfer switch to the main panel, from the main panel to the inverter/charger, then AC is passed through the inverter/charger to the sub panel. My sub panel feeds the microwave and a few lights and recepticles. The items that work from the sub panel are the ones that will work when using the inverter function.
Generator power functions the same as shore power.
Battery power feeds the previously mentioned items that are directly connected to the batteries plus the items in the sub panel.
Batteries are what I always check first. One of my biggest hints is that my step quits working when my house batteries get low.
I have some concern about some how your batteries are connected. The 25v measurement and the statement that you hooked them up like the previous owner are not the same "as I know they are right". Again, I made a diagram for my coach that shows all the power. You should note that the house batteries are connected in 2 parrallel pairs of series wired batteries. To write that another way, 1 & 2 are in series, 3 & 4 are in series, the the 2 pairs are connected in parrallel. This nets the 12-14 volts expected.
My coach also has a sticker on the wall of the battery compartment that shows how the batteries should be connected.
On my recent trip, I had some generator problems which lead to some house battery issues when I had a long travel day. To solve the battery issues, I first made sure they were properly filled with water (should be serviced monthly). My control panel would show readings in the low to mid 12s when my step stopped working. When I hooked up to shore power at the end of the day, my inverter would alarm when trying to recharge the house batteries from their low state. I solved the problem by using a auto battery charge on the house batteries while I camped overnight. After a couple of days of struggle, I realized that I was straining the batteries and the inverter/charger by setting up (jacks and slides while the AC was running) before I hooked up to shore power. My house batteries are 6 to 7 years old, so this might be a sign that they are near end of life. My inverter is OK.