AC meters read RMS values. Unless the output is a true sinewave, the meter will be off.
If you have an AC generator, and you're half- or full- wave rectifying the resulting output, the reading will be all wonky as the signal doesn't go pos and neg.
A 16 volt (peak) full wave rectified signal will most likely read about 6 to 7 volts RMS on an AC voltmeter (maybe a bit more), since the meter will self-center at half the average voltage value, and read an RMS value of the resulting voltage swings. That 16 volts will most likely be fine for charging a battery, though, since the peaks are all positive, and any load will smooth out the teeth.
I would suggest putting an old battery onto the outputs, and then see what the meter reads.