Brick has interesting charging/battery behavior

Charging the brick from 40% to 100% takes just as long as charging from 90% to 100%. I have 2 bricks and when I charge them together they often finish charging at the same time. Obviously with different percentages. Strange.

Also I don't know if it's Surwish crossmix or what but the sleep functionality is amazing. I've left this thing sleeping for around a week and lost frighteningly little percentage. Enough to make some android phones blush.

I imagine the two are connected. What black magic is TrimUI using lol?