XPS 9500

I have a Dell xps 15 9500 with bios 1.15.1  

The problem is, my system charges to 100% overnight when my bios power settings are custom set for charging between 70% and 85%.   So it should charge up to 85% not 100%,  and if charge drops below 70% it should start charging.

The day before, my system battery was almost completely drained to about  5% when I got a warning.  Then I left it plugged in and it charged to 100%.   Why is this? is it a bug?