There is most probably nothing wrong with your laptops neither in software nor the hardware side.
I got the same problem and no one could help me and the SupportAssist didn't detect a problem either.
So what is the solution? Well its simply the Dell Power Manager battery setting is set to a default of Adaptive charging,meaning it does whatever it wants whenever it wants.
SOLUTION:
1] Either install/update Dell Power Manager [if applicable]
2] Open Dell Power Manager from Start
3] click the blue settings button on the right of the giant green battery under the "battery settings:" label
4] Read the pop up you will understand where I am getting at