With a good multi stage charger that maintains the proper voltages the battery will vent very little until it reaches the end of life.
But 3 things are required for this to occur:
1. The charger must be designed to charge your batteries to their mfg specs vs some generic battery type - flooded being the most common.
2. The charger must be adequately wired to the batteries which means that it is very close or very heavy wire is used. Many RVs fail in this regard.
3. The charger must have a remote temperature probe on the batteries unless you are always at the optimal temperature per mfg specs which is about 70F+. The temp probe provides the necessary data for the charger to adjust the charging voltage.
I've seen my float charge vary from 13.1V to 13.9V depending upon temperature.
