The computer is running under the battery health mode of "Best battery health". Unplug the AC power, use the computer battery till dropped to 8~10%. The battery health mode will auto switch to "Optimize for battery runtime" see Fig.1 and cannot switch back to "Best battery health" until charge to 50%.

Fig.1

The above symptom may occur under the following systems:

IdeaPad Yx7x

On the following software:

Lenovo Energy Management 6.0.2.0

When the battery is at low level, the battery health mode will automatically switch to "Optimize for battery runtime" and cannot switch to "Best battery health" until charge to 50%. It is due to the special design for Yx7x. When the battery is at low level, "Optimize for battery runtime" mode will enable battery to last long runtime.