Vmoto and Social Media, page-1562

"I don't see how 220Vdc can be used to directly charge a 60V battery."

MTV electricity is a really interesting and sometimes quite simple beast. The answer to your question comes back to the formulae

P=VI where P is Power, V is Voltage and I is current.

The output of the battery on the bike is 60 V and has a maximum power storage which is VxI, when charging, the main limitation is not to overheat the battery, it is the current (I) that produces the heat hence a large amount of power can be transferred (to a battery in this case) quicker and more efficiently at a higher V and lower I.

Charging is just getting power into the battery, the battery discharges at 60V.

I hope that helps.