well.. I have a breakthrough!
I fully charged the T62 and then read for about an hour and then left it for another 8 hours... and the battery was on... 99%! So I turned it off and on and read a little more, put it down and shortly after it turned itself off as it was supposed to in the settings.
Now, almost 24 hours later the battery is still @ 99%!! Both "better battery stats' and 'gsam battery monitor' agree it's still 99% charged.
So, realistically, something has gone wrong and the battery will suddenly die unexpectedly at some point
Still it's nice to have the fun experience of feeling like it's my old NST!