Mel, The 3 stage chargers do have the higher voltage as you indicated and as you have kept your properly adjusted they perform well.
My history is in commercial battery plants where most are float service which are constant voltage.
My statements are for basic single mode charging units but float current and voltage are universal regardless of charger and a few tenths of a volt can change float current to something that will cause gassing while floating.
Easy no brains thing is if batteries are bubbling after fully charged...maybe a week on shore power without any loads then one can assume charging voltage is too high...Assume used correctly as one next needs to get out voltmeter and confirm and follow up as needed.
Tony & Lori
1989 Country Coach Savannah SE