That is terrible advice, given by someone who has a limited understanding of the battery's function in the charging system. The battery acts as somewhat of a "shock absorber" in the system, leveling out voltage spikes as they happen, and also determining charging voltage to some extent. I have seen voltage spikes of 100 Volts or more on an oscilloscope when a battery cable is disconnected with the engine running. If you've got a radio with solid state electronics, or an alternator with rectifier diodes, goodbye electronics! The voltage produced by the charging system will only rise high enough to force a charge into the battery- - - -the "voltage regulator" function only establishes the highest voltage the generator produces when opposed by a fully-charged battery.
Against a low battery, or immediately after starting, the voltage might only be 12.5-13 volts, because that's all that's required to make current flow into the battery. As the battery recovers its charge, the voltage will rise, and the regulator should limit it to 14.5-14.7 volts if the battery is fully charged. Use a hydrometer to check the concentration of the battery acid- - - -that's the ONLY way to determine if its getting a full charge. Full-charge specific gravity should be about 1.265-1.300, while a completely discharged battery will have a S.G. of 1.000-1.100 or so. BTW, a badly discharged battery can freeze solid in cold weather, so never leave a poorly charged or discharged battery exposed to freezing temperatures!
Jerry
