Batteries normally bubble slightly during charging, but 2 amps is a pretty low (harmless) charge rate. At 2 amps charge rate, you would see occasional bubbling. With a sealed battery, I don't think you would see much from the vent at a 2-amp rate. At higher charge rates, boiling and spewing indicates sulfated plates that may not recover with charging. The charge rate that causes vigorous boiling with sulfated plates depends on how 'entrenched' the sulfating is. A battery that has been standing dead for along time- several months- may not recover with charging, and would likely boil pretty vigorously at 15-20 amps charge rate. Charging voltage is another indicator of sulfated plates- for most any 12-volt battery, 15.5 volts (7.75 volts for a 6-volt) at any charge rate above a few amps of charging current indicates a sulfated condition. From your description, either you had a shorted cell, or the battery was badly sulfated. Without a voltmeter to watch during charging, and not without the battery, this is all speculation.
Harvester
