If you suspect that the battery gauge is not accurate (e.g., you hear a series of monotone beeps when turning the steering wheel right), you can reset the battery gauge to its default calibration. Do this by holding the steering wheel right continuously. First you will hear the regular battery gauge beeps repeatedly, then 1 beep (calibrated for 10 mile battery), then more battery gauge beeps, then 2 downward pitch beeps (calibrated for 15 mile battery), then more battery gauge beeps, then 3 downward beeps (calibrated for 20/27 mile battery), then more battery gauge beeps, then 4 downward beeps (calibrated for 40/55 mile battery). You should let go of the steering wheel once you have gotten past the number of downward beeps corresponding to the battery pack size you have on your Metroboard. Now the battery gauge will be restored to its default calibration.
DUAL DRIVE NOTE: On the dual drive there is just one battery gauge setting (for 25/35 mile battery). You need to check the battery gauge several times in a row till you hear 4 downward beeps. This will then restore default battery calibration. Note also that on the dual drive this will restore both controllers to Acceleration Skill Level 5 and Braking Skill Level 1. This may be necessary also in the case where one controller is out of sync with the other, which can sometimes happen by accident. So if your Dual Drive is behaving strange, you should follow this procedure as well to resync both controllers.
Note: If you check your battery gauge more than 3 times in a row (without using the gas or brakes in between), you will accidentally reset the default battery gauge calibration to the 10 mile battery, so be careful to avoid this, or you will have to recalibrate per instructions above.
See also video below starting at 6:53