A battery should go to 13 when charged and it’s gonna have to hold 12.7 .8 to fire 12.6 but I don’t think 12.11 gonna work, it’s probably not your charger to me it just sounds like that battery ain’t taking it. Maybe someone will chime in and say bull ****e that ain’t right, but it just sounds like a battery, like you brought it back to life 2 months ago but she’s barking and ain’t eating a charge now. Hope I’m wrong