I am on my second 12v motorcycle battery in a couple of weeks. Will a faulty regulator, ie too higher volts, cause this? Also I have upgraded my ct110 to a 160cc, all works well for a few days, then gone.



2 Answers 2


Yes, a bad regulator will cause your motorcycle battery to be overcharged. This is a common failure because of the way motorcycle alternators work.

Measure the battery voltage while the engine is running. It should be between 12V and maybe 14.8V max. Now rev up the engine and see if the voltage shoots above that. If it gets to 15 Volts or more, it is overcharging your battery.

There's a good article here that explains how motorcycle alternators work: http://www.electrosport.com/technical-resources/technical-articles/how-motorcycle-charging-system-works

But the point is this: The permanent magnet alternator in motorcycles outputs higher and higher voltage (and power) as the engine revs up.

The voltage regulators job is to limit the voltage to about 14.4 Volts by dissipating the extra power that is not get used by the battery, lights, etc. That's why motorcycle regulators have big metal fins and should be out in free air. If this regulator fails, then all that extra power gets pushed into overcharging your battery.

This is different from an automobile alternator where the regulator throttles the amount of output voltage put out by controlling the current through the rotor electromagnet. In a car, the most common failure of the regulator in a car is that it undercharges the battery because it cannot feed enough current into the rotor.


I believe you mean alternator. It charges your battery when your motorcycle is running.

The alternator needs to output 12.6V to 14.4V when it's working fine, use a multimeter to check it out.

  • 2
    No, he meant regulator.
    – SteveRacer
    Commented Aug 5, 2017 at 2:02

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