Most often hooking up your battery wrong is the reason for blowing the in-line fuse close to the battery terminals. This also blows the two REVERSE POLARITY fuses mounted in the 12VDC distribution panel.
Just takes one quick spark haha...
having a multimeter around solves all of these problems. A fully charged battery will read 12.6VDC at the terminal and when you hookup to shore power this DC VOLTAGE should jump up to 13.6VDC. This tells you everything is connected and working between the on-board converter/charger and the batteries.
The inexpensive multimeter is available from WALMART and LOWES and any number of auto parts places for $7-$20. A must have item for all RV'ers.