Does the generator not turn over (crank) when you try to start it,
or does it crank but won't start?
Have you checked to make sure the battery is charged (I realize it's a new battery, but it wouldn't hurt to check that).
You've probably got two battery switches somewhere, generally these are near the main entry door. Either just above the steps or in a nearby cabinet.
The labels change by mfg and year, but they will be named something that indicates that one switch is for the house a battery, and the other switch is for the engine battery.
Are both of those switches turned on?
Do your unit have a 'battery boost' switch on the dashboard?
If so, try pushing that switch while attempting to start the generator.
This is a two person job if these boost switch and the generator start switch are not close together. The boost switch is only 'on' while you're actually holding the switch down.
Does the generator have both a remote start switch and a start switch mounted on the generator? If so, have you tried starting from both locations to see if the 'other' location will start the generator?
2013 Winnebago Sightseer 36V