Cause of this issue

1. After upgrading the new firmware, the old firmware is returned, resulting in incompatible data structure and loss of calibration data.
   
2. An irrelevant file is written to the device U disk, causing the calibration data to be overwritten
   

Solution

1. Upgrade to the latest firmware, firmware files can be found on the toolkitRC website, navigate to your charger and go to the downloads tab to find all the firmware files. https://www.toolkitrc.com/.  Instructions on how to update firmware are on the website, and usually included with the firmware download files.
2. Once firmware is updated, Enter the manual calibration mode (M6 press the exit button when the LOGO interface is displayed, M8 and M8S press and hold the turntable to start).
   
3. Move the cursor to the factory value and confirm.
   
4. Calibrate each voltage (input, output, balance port).
   
5. Save and exit to complete the repair
   
6. The unit should boot normally now.
   

Extra Info

Pay attention to the current accuracy during use. If it does not seem right, perform current calibration.

The calibration steps are as follows: 

1. 1. Set the 5A current to charge the battery, connect to the meter, and measure the actual current.
   
2. reboot into the manual calibration (M6 press the exit button when the LOGO interface is displayed, M8 and M8S press and hold the turntable to start).
   
3. Set the current value to the actual current value and complete the current calibration.
   
4. Save and exit
   

For more info see How to calibrate the Voltage on ToolKit Rc chargers