It might help if you tell us which 2 batteries you replaced. Chassis or house, or one of each. Are all batteries hooked up exactly like they were? Have you checked for 12 v at your battery isolation solenoids? There is also usually a large circuit breaker in the line from the batteries, check that power is going through them. Which battery was left, and is it paired with one of the new batteries? That can be an issue in that the old battery will keep the new one from reaching full potential.
Since you had power until you disconnected shore cord, it could be a fuse or circuit breaker on the outside of your Converter/charger. What happens when you plug in shore cord, is 12 v power restored? If so, then likely the batteries are not hooked up correctly or a bad connection and you are running off the Converter/Charger only.