laptop charging 2% an hour

I have latitude 5591, 1.5 years old. After an BIOS update 2 days ago, my laptop has been charging much much slower, I noticed yesterday that after like 3 hours it had charged only 40 %, but today after 2 hours it has charged 4%.

I have had battery problems before,a few months ago it started to display inaccurate battery percentage where it would suddenly jump from 30 to 7 % , I did a full charge and discharge, after that it was better, but the charging indicator has randomly been flashing even though it is not plugged in.  

What should I do