Dell 5559 laptop is not charging when it is below 50% battery level.

My laptop is not charging when it's below 50% battery level and turned on. But if I completely shut down my laptop and plug it in then its charges continue to 100%. I tried to update the battery driver also updated bios and installed a new battery and charger but it didn't fix anything. And if I unplug my laptop from the wall it becomes unusable for 10--15 sec by slowing down completely even if its 100% charged and max performance mode on battery. what should I do now?