After poking around for a while, I finally figured out how to change the charge threshold on a ThinkPad computer without Power Manager GUI installed. This has been tested to work on my x220 tablet. Here is how:
Install Power Management Driver (tested with v22.214.171.124)
Install Lenovo Settings Dependency Package (v126.96.36.199). This package actually contains the necessary code to interface to the battery controller chip.
Open the Start screen with the Windows button, then type regedit.exe. Right click on regedit.exe and run as administrator.
Find the registry key [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Lenovo\PWRMGRV\Data].
Now you should see 4 entries that are currently set to 0: ChargeStartControl, ChargeStartPercentage, ChargeStopControl, ChargeStopPercentage.
The first 2 entries, ChargeStartControl and ChargeStartPercentage, change the starting charge threshold. Double click on each of them and change them both to your desire starting charge threshold. For example, if you want to start charging the battery only when the bettery level is below 40%, change both of these entries to 40. Also, make sure you have Decimal selected as the base unit.
The second 2 entries, ChargeStopControl and ChargeStopPercentage, change the stopping threshold. Double click on each of them and change them both to your desire stop threshold. For example, if you want to stop charging the battery at 80%, change both of these entries to 80 (base in Decimal).
Restart your computer. Somehow, the values in these registry keys get written into the battery controller after restarting the computer.
Note : Please proceed with caution while tinkering with the windows registry.A better option is to take a backup before you perform any changes