Being new to caravanning and due to the pandemice my van has been in storge for a while now. I read recently that if the leisure battery dies it will be useless so I decided to take it out my van and bring it home to keep it charged. To my horror when I put it on charge using my car battery charger after an hour it started spluttery battery acid everywhere! Have I killed my battery? I have attached a pic showing the hole on top of the battery (which is meant to be sealed and maintenace free?, Any advice would be much appreciated. Thank you