5 V and 12 V output for ebike

Is it possible to use standard wall chargers on ebike when running the bike like 66 - 75 V DC? Can I use for example normal 5 V mobile phone charger to convert the voltages from 75 V DC to 5 V DC?

Normally wall charger input is something like 100 - 240 V AC but does it work well when using lower DC voltages? What is the minimun DC voltage which is possible to use?

I know that on 72v 20s they do work. They could work on a bit less but id try it out, it shouldnt hurt anything.

It should work. I did some testing with the usb power supply that comes with the nintendo switch, it ran from as low as 20V. Make sure you test with both polarities, sometimes it doesn't work when you hook it up in one direction but if you swap the wires it will work.