Bad li battery pack, what am I missing

[Seekonk]

My laptop came up with a notice "recommend replacement of battery pack".  I've been expecting this for years, date code on the computer is 1110.  They are cheap enough so I ordered another.  I've been scavaging batteries from these packs for years so thought I might rebuild this one as a spare.  I've built a micro based li tester and bad batteries have always been easy to spot.  Popped the cover on the pack and each battery measured 4.27V, that seemed a little high for a pack that had been pulled out for days. Then I used a 3.9 ohm (about 1A) resistor as a load, 3.59-3.64V after 30 seconds. Unloaded the batteries still 4.26V after load test.  Seem pretty good to me as I only run on line power. Am I missing something or does the laptop just have a timeout after so many years?  If so, is there a reset?

[Ian.M]

Do a timed  constant current discharge test down to 3V/cell and compare with nominal capacity.  Calculate the current to use from the laptop's specified running time and the cell capacity.

To get a laptop to reset the S.O.C. statistics stored in the battery's ID chip and recalibrate capacity, one normally has to do a full uninterrupted charge/discharge cycle at least once.  If you always run on mains power it wont have reached the max discharge threshold very often if at all so the estimated capacity will be very unreliable.

[Audioguru]

An old lithium battery can hold its unloaded voltage for many years. Its age deteriorates it so its voltage drops when loaded but goes back up to normal voltage with no load because its internal series resistance has increased.

I have Ni-MH cells that do the same. A good charged AAA cell can provide 7A to my current meter that shorts it but an old charged cell with exactly the same unloaded voltage cannot provide 1A.

I agree that the capacity of a Lithium battery that is stored fully charged, has been discharged to a voltage lower than about 3.2V or has been discharged and charged more than about 500 times has reduced capacity.

I won't talk about the lack of quality (too much rice powder in them) of Chinese batteries.