Assuming you accept risk of heating/fire/explosion to test (carefully):
Only charge at low current to 3.1V max, discharge to 2.0V min.
See if you can log the charge in vs charge out.
If it is rechargeable you should get related results to a typical 18650 cell (but lower voltage), eg good energy efficiency.
If not rechargeable, stored capacity will be poor vs label (maybe <50%, you said you got 6Ahrs vs 22Ahrs already) + you may get above heating, swelling, etc.
Shelf life when new is good (~10 years & only very low self discharge (eg something like ~1%) apparently.
Application was for only occasional use & in sealed bottle so I'm pretty sure now this one is not a rechargeable one.