You will not charge if the dc volts are less than the battery volts. If there is energy there and just the volts are too low then you could boost the volts if you have the technology, If there is not enough energy from the wind source it may be pointless.
If it is a commercial device it will be chosen to cut in when there is useful power from the wind and below this point boosting the volts may get you nothing or stall the blades. If it is something you have built and you have got cut in speed wrong then boosting may get you somewhere.
Input volts above battery volts will be ok. Wind turbines have a high source impedance and the battery will determine the volts and the source impedance will determine current.
The source impedance is composed partly of the electrical impedance of the generator and partly by the limited power available from the blades. Battery resistance is too low to be worth bothering about.
This is not the same situation as the bit you mentioned later about paralleling a 12v battery with a 24v one. In this case the only limiting factor is the very low internal resistance of the batteries and connecting these in parallel will burn something, wires, battery lugs or explosive gas. All common charging systems have restricted current capability but using one battery to charge another will cause damage unless you include something to limit the current.
Flux
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