6 volt vs 12 volt charging

Thanks for the help, folks! A couple answers, then something for me to check tomorrow. I do have a 50 amp RV. My home storage is a dedicated 30 amp circuit off my tool shed. So I assume my converter is designed to handle up to 50 amp service. Second, I regularly saw 14.2 or so when charging the 12 volt batteries. Normal voltage was 13.4 or 13.6 I did have a 15 amp fuse blown in the inside fuse panel. But it was #13 to the refrigerator. Seems like that fuse blows nearly every time I disconnect the batteries and hook-up again. Anyway, It's too cold and nearly dark now to do the in-depth checking I need to. I reset the "converter's" breaker in the main box, and tried to check the 50A line fuses on either side of the shut-off switch. Tomorrow, I will disconnect batteries and take wires off line fuses and check them. With AC if you check both sides of a blown fuse you read say 120VAC, if the fuse is good you read 0 On my DC setting I read 0 on both fuses. Again, I will check tomorrow with fuses disconnected.

I did have 6.5 on the new batteries, each, and 12.7 hooked together before install.

Sorry for the edits I am reading the voltage at the battery terminals and a meter plugged into a cigarette lighter type fixture inside the RV. Same reading.