Yamaha 2400 generator's on-board 12V charger

The charger output on this and possibly all small generators is unregulated and unfiltered. It's produced from an AC winding run through a full-wave rectifier, and nothing else. Depending on the voltmeter, it might read the peak, average, RMS, or almost any other voltage that it decides the DC voltage of this output is. When connected, the battery acts as a filter and changes the output to better DC, still with a lot of AC ripple, and different voltmeters will still interpret this differently. The Honda eu-series manuals say the charger output should be used to charge automotive-type batteries, and nothing else. They also admit the the output is unregulated. I've read at least one publication that suggests using the unfiltered output would bring a fairly quick death to an AGM battery. A FLA battery is apparently perfectly happy with the dirty power, and low end battery chargers have been providing this since the dawn of battery chargers.