I have a schumacher sc2500A.
It often, without any discernable reason, will take the battery to and above 16.4 volts on the 12 or 25 amp setting, and hold it there for more than an hour with the battery burgling burping and smelling like burning rotten eggs.
This is extremely abusive to lead acid batteries, and if they are overfilled when undercharged then the charger takes them to 16.4v, they will bubble up a flood.
Most chargers will cause spillover when the battery is overfilled, but a charger taking them well above 14.7v will make the issue much much worse.
Check the voltage when charging, if you are finding it to climb well over 15 volts via a multimeter on battery terminals, as I suspect you will, then consider returning the charger, if you still can.
Also the % state of charge display on these garage chargers is so laughable as to be completely ignorable, and the voltage on mine was also considerably different than actual battery voltage.
Hers a schumacher video overcharging at 15.9v. These have no equalization feature. Not sure how Schumacher has been able to get away with products which can so seriously overcharge, when all other makers of consumer grade garage chargers err on the side of well undercharging and doing smoke and mirror marketing saying how great they are.
https://www.youtube.com/watch?v=5BF8FB__iR8&list=UUoPqTkOluQsuu3RpGnxVwFw&index=41
