the problem with the ebike batteries usually are, is that they are not rated for such high amp draw.
they can use cheaper 18650 cells.
because of this drawback, I built my own 18650 battery pack,
I documented everything along the build process.
(note: I planned 15p first, but that was too little of capacity so I upgraded to 20p later. If I’d built a new system today, I’d go for 25P )
See it here: 13S15P Battery Pack Build
and then follow up here: Follow up post: Case for 13S20P Li-Ion Battery Pack