BMS bad?

[duneslider]

My understanding of State of Charge is wildly different from this. https://image.slideserve.com/666777/state-of-charge-l.jpg Looking at the things I've read, 80% should be around 12.4-12.5V OCV/resting (sources differ). What's even more odd is that when my battery was down around 12.6V resting, the truck would say it was about 60-65% SoC and things behaved oddly. Frankly, I'd agree that there is probably something screwy going on. Interstate Batteries mentions 12.64 being 75% SoC, but they don't specify whether that's AGM or something else.

Yeah, I had a brain fog yesterday...they are Calcing SOC based on Fully charged voltage and dead which is about a 1-1.1v swing, so 80% would be roughly .2v down from full. Without knowing what values they are actually using it would be hard to say what they are considering 80% and then on top of it any SOC measurements on a battery that is in a running vehicle is guesstimating at best. I guess, I am still surprised they would only be shooting for 80% soc. I guess if I cared enough I would go measure what it was doing but I just put a charger on it a few times a year and call it good. My battery is from 2020 and seems to be okay, though probably nearing the end of it's life.