Just to admit something odd I do in public. I've started using my lithium powered devices between the 40%-80% charge range. i.e. I plug it in when it's at or around 40% left charged and unplug it when it's 80% charged or around there. I'd read that's what Tesla drivers recommend for maximizing the life of their batteries. Don't know how much it translates to phones/computers. 40% of 20 hours is 8 hours...