Unfortunately the issue is complicated by the fact that different types of meter work in different ways and usually when you grab a meter you have no idea what it is going to do if you use it for other than it was intended.

AC presents many problems once you depart from a sine wave at 50 or 60Hz.

True rms meters are predictable as they all measure the same thing but the answer may be far from what you expect if the waveform is way off your expectations.

Cheap ac meters are very unpredictable, although most full wave rectify the ac to dc, those that do that measure the mean value instead of the rms for a sine wave.

It has been standard practice to scale them to read rms on a sine wave. They then agree with a rms meter on a true sine wave and for working with normal supplies that is good enough.

Unless special measures are taken they all run into trouble at low volts where the rectifier drop is considerable. Cheap analogue ones have a special scale that is nonlinear for the low range.

Cheap digitals tend to have the low end restricted to about 20V and they hope you don,t try to measure very low volts. At 3V some can be badly out.

All AC meters have problems at low frequency, analogues vibrate the pointer and digitals do all sorts of strange things as they sample at different points on the ripple.

Measuring dc is easier, all normal dc meters measure mean. If you use a rms meter on smooth dc it will be ok but will read high if there is riple.

Bridge rectifiers are not perfect devices and at very low currents they can do odd things. The high impedance digital dc meters can give silly results on rectifiers with no load and if there is capacitance in the circuit they can often read up towards the peak and not the mean.

Probably the best advice that I can give for wind generator work is to only ever use a meter on the ac range to measure the ac voltage on open circuit, don't trust it too much at low volts unless it is true rms and even then it may be wrong if the waveform is very bad. Beware of any meter at very low frequencies.

Normally the waveform of air gap alternators is good enough to assume that it is a sine wave for normal use, Some iron core machines may be way off a sine wave.

Never use an ac meter to read the input voltage to a rectifier on load into a battery, the waveform will be so far off as to make it meaningless.

Never use a meter on the ac range on the dc side of a rectifier, many will give a reading and it is usually very high, some will not read at all but most modern ones will read and it is meaningless unless you know exactly how that meter works and how it is scaled.

For measuring dc volts after a rectifier it is safer to connect a bit of resistance to provide a slight load to keep the rectifier happy and prevent stray capacitance from charging. Values in the region of 1k ohm should cover all normal cases. Often you will not be very far out if you ignore this, but if you look with a "scope" to see what is going on, you will see things that are not good.

I hope this helps, but it is a very complex issue and without knowing the exact meter used you can't be sure what is going to happen.