Can you Charge a 60 or 72V Battery Pack with "a" 12V Solar Panel?

[ARod1993]

I am planning on building a Li-ion (cylindrical cells) 21700 battery pack for a 60V system for my future e-scooter.
And I live off-grid. Can you use a 12V or 24V solar panel to charge a 60V or 72V battery pack? I thought you have to have a solar panel (or solar panel"s") that has 72V output in order to charge a 72V battery pack.. The battery cell is 3.6V nominal, 4.2V max.

And charge time does not matter to me as I don't mind charging for a few days without using the battery. Anyone?

You absolutely can; it's just going to require a DC/DC converter and an MPPT controller between the panel and the battery charge input. The MPPT controller essentially adjusts the duty cycle (and thus the input impedance of the converter) to match the voltage and current that gets the maximum power out of the solar panel, and then the DC/DC converter to go from the MPPT output to the battery pack voltage. Ideally you'd want that second DC-DC converter to be able to operate up to 84-85V so it can fully charge a 72V pack, and ideally it would also be able to operate in constant-current and constant-voltage output mode so that it can charge the battery properly.