Morris Minor Owners Club

Anyone had any experience of a hissing battery, first noticed it while on charge in the shed, it has two vent holes on each side, one was missing, removed the other one that was under slight pressure and hissing stopped. Noticed today after comming back from a run that the battery was hissing again and rather warm. There appears to be a build up of gas that needs and struggles to escape while being charged, never come across this before, concerned that battery is faulty and possibly dangerous. Any thoughts!!!

Sounds like the battery is being overcharged - what volts does it read when engine running at say 2000 rpm