Aircraft use 400hz, as the alternators can be smaller, (lighter) but the associated output is then subject to wide fluxuations in output.
Why would it be subject to such fluctuations? In my experience in the 747, generator output is VERY stable once power transfers are complete after start...
Besides, if a charger is rated at 100-240V, why would a fluctuation matter to the output? I suppose the charger electronics could fail early with repeated fluctuations, but why would they carry over to the battery being charged?