I tried it in parallel. Is that incorrect? I used this method 2 https://www.onallcylinders.com/2016/12/13/3-ways-bring-deeply-discharged-optima-battery-back-dead/
I don't have a specific charger for AGM batteries. Maybe I will bring it to someone who does.
I really don't want to spend $300+.I think I paid under $150 for this one.