Charge a 48V battery with a 20V solar panel

Hi,
I wonder what device I have to use to charge a Li-Ion 48V battery with a 20V solar panel ?
MPPT for 48V battery seems to be used only if the solar panel voltage is higher than the battery voltage.
Thanks in advance

Don’t think Victron makes anything for this situation.
However, there is this:

I own one, but have not used it yet.

Step up dc DC as suggested

or put PV panel in serial with battery and use it as input to MPPT (75V or 100V voltage rated) to charge same battery back

Interesting, thanks.
But, the tuning of battery charge voltage seems not very precise and it is not digitally connected to be able to monitore the charge power

You are quite correct, it is really meant for infrequent use in a pinch, not as part of a real system.