OEM one is Yuasa YTZ-10S
https://www.amazon.co.uk/Yuasa-YTZ1...pID=51nGQptZORL&preST=_SX300_QL70_&dpSrc=srch
Sounds like your charger is bust & has just been shorting terminals and discharging. Worth trying to charge with a functioning charger. Should be about 12.5 to 12.8 V when fully charged with no load.
https://www.amazon.co.uk/Yuasa-YTZ1...pID=51nGQptZORL&preST=_SX300_QL70_&dpSrc=srch
Sounds like your charger is bust & has just been shorting terminals and discharging. Worth trying to charge with a functioning charger. Should be about 12.5 to 12.8 V when fully charged with no load.