Laptop works better on battery than on mains.

Hello, I have such a question, why does my laptop run on battery better than charging? Let's say when I play a game on charging a laptop, I have a fps of 40-60, I detach the cable, the fps becomes 70 and higher. In the power settings are identical, that with the charge that without high performance and in the settings radeon is high performance.
Windows rolled back to the original state.




Radeon software version - 17.5.2

Radeon Software Editorial - Crimson ReLive

Chipset graphics - AMD Radeon (TM) R5 Graphics

The amount of memory - 1024 MB

Memory Type - DDR3

The core frequency is 800 MHz

Windows version - Windows 8.1 (64 bit)

System memory - 12 GB

CPU Type - AMD A8-6410 APU with AMD Radeon R5 Graphics