Hello so I own a Dell D531, I bought it last year for doing basic stuff like web surfing and youtube watching, but I really can't use it for any of that because the cpu decided to always run at 798mhz when unplug it and it only does it when unplug it, runs good when it plug in. I had worked on may dells and other brands but never had encountered something so irritating about a laptop in my life. I hope someone can help me or answer why it does this, and if it a dell thing and can't be resolved then I can only sell it for parts since it pretty useless when it runs at 798mhz when you unplug it.
A couple of things to check. If you go into CP>Power Options>change Power Plan settings, look at what your min and max CPU percentage is while running on battery. You may need to change this setting or switch to a high performance Power Plan. Also, some Dells will throttle the CPU if the battery is going bad or battery remaining percentage is set too high. Also check in the Bios for any settings that may affect performance while on battery.