You will need a BMS to balance charge 20S directly. This one is programmable and looks promising at a low cost and I think they have a 20S version: https://www.aliexpress.com/item/24S-Lithium-Ion-battery-Smart-BMS-with-UART-communication-port-and-86-4V-or-88-8V/32778195210.html
Or, you can do what I did for my 20S setup which is have 2 10S blocks connected in series for use and then I have another harness to put them in parallel for charging with my 3010B.