With 20% I would expect it's at 3.4 or 3.3? Anyway since it's .1 difference so it's about 3% difference.
I wouldn't recommend recharging at 20% remaining though. Generally a battery should be recharged at 3.5 v, I read it somewhere but I forgot why. Sorry.
Yeah 3% and I was figuring in the shut down voltage of 15% as well..close enough I guess thank you bro.