You realize batteries can fail in ways other than capacity, yeah?

The amount the battery holds (capacity) Is not the same as current.

One is how much it can hold, one is how much power it can supply per second until the capacity is depleted.

Anything from heat, cold, or chemical failure in the battery can cause this kind of issue, you can have over 100% batt health and the battery can still be a lemon if it drops cells or electrolytes cause expansion.