Get a proper testing device, there's an affordable electronic load / battery tester which can be had for little money:
- https://www.aliexpress.com/item/32856429623.html ZKE Tech EBD-M05.
- https://www.aliexpress.com/item/32664964301.html ZKE Tech four wire holder.
Features PC software which plots discharge graphs. I have one right here still untested, waiting for my holder.
More information here: ZKE Tech EBD-M05 help