I am going to show you how to calibrate the voltage on the Traxxas EZ-Peak Plus 6 amps charger: #2933
Here are the steps:
1.) Power off the charger.
2.) Press and hold the "-" and "enter/start" buttons.
3.) Power on the charger. (you will hear 3 beeps in a row). Keep the buttons pressed.
4.) You will enter into the calibration screen where the voltage detected by the charger is displayed on the screen (voltage on output leads).
5.) Attach any battery to the output leads of the charger.
6.) Using a digital multimeter, correct the reading of the voltage by pressing "-" or "+" buttons till the reading matches with that of the multimeter.
7.) Press "Stop" when you are done.
8.) Your charger is calibrated now.
**Remember to use an accurate voltmeter.
Thanks for reading.