Erratic Voltage Reading

Did you used a digital meter ?
If so it may be erratic because:

Generators produces 12~15 volt with voltage regulator. It also produce very short high voltage spikes (300 ~ 1000 volts)"brush to commutator mechanical contact sparks" which are undetectable with usual test equipment. The votage regulator also produces short high voltage spikes when the contacts opens it creates back EMF of several hundred volts.

That said: Many digital multimeters see those HV
extremely short spikes and tries to measure and display the result which causes erratic and unstable display. Radio frequency interference from HV ignition system may also cause induction in the test leads and cause same results. We must use a digital multimeter designed for automotive measurement purposes.

A $10 ~ $30 analog tester (with needle) may be far more accurate than most domestic DVM for battery charging voltage measurements.

My 2¢

Joe Ferguson

A sulfated battery will allow greater voltage but the charging current won't taper to zero like the good battery will when charged with 14.2 volts.

When overcharged the battery electrolyte will bubble, looks like its boiling, but its not that hot. Its the water being dissociated into an optimum mixture of hydrogen and oxygen for an explosion. If the electrolyte level goes down in half a day of running, the regulator isn't regulating or is regulating at too high a voltage.

Its preferable to replace the lost water with distilled water, tap water is not beneficial for battery life.

Gerald J.

2.) Are you checking the battery voltage with a DIGITAL voltmeter? MANY digital meters can't cope with the electrical "noise" produced by the ignition and charging systems on these old beasts, and will give erratic readings, making folks think the CHARGING SYSTEM is acting goofy, when the digital meter is actually what is goofy.

3.) If the voltage is REALLY high, and erratic, it points to a voltage regulator problem.