My charger said it was a 6 volt and all my others read 12 and charged fine.So after 4 hours it still read 7.9. So for fun I put in on normal battery charge and on the wing nut post and what you know it started charging so dont throw it away just yet try it for fun.
https://www.amazon.com/Optima-Batteries-8016-103-BlueTop-Starting/dp/B00075OSCO

