old sparks
Member
If you are hearing it crackling and bubbling I would take it off the charger unless it is a smart type charger like a Battery Tender or Yuasa. Otherwise you run the risk of overcharging it which can buckle the plates. Most sealed batteries come charged and can immediately be put in service.
^^This^^
If you hear bubbling and crackling in an AGM battery, you are likely charging it too fast.
https://en.wikipedia.org/wiki/VRLA_battery