I've soldered directly a Li-Ion 1035mAh (10+ years old, NOS, no swollen signs, made in Japan). Charged it at first very slow, at 5mA then at 10mA for a couple of hours, then at 50mA for another about 20 hours, until the battery was floating at 4.2V and was drawing less than 3mA charging current instead of 50mA.
Didn't measure the capacity after charging. Judging by the charging time and charging current, it probably has more than 500mAh. My guess is it still has 70-80% of its nominal capacity. Even at 50% it will be twice the capacity of a good CR2032, so the remaining capacity doesn't matter much.
4.2V seems a little too much judging by the LCD contrast. Next time I will charge the battery at only 3.8V. There is not much charge stored at higher voltage anyway, probably less than 20%. Most of the charging time was spent between 3.5-3.8V so I guess that's the voltage where the most energy is stored.
It is all now about the self-discharging rate of the battery, which I didn't measure. Unless the self discharge is horrible, it should last for about 10 years before needing a recharge.
Well, probably not 10 years, but I've found a few very old Nokia with battery about half after 10 years or so of storage. Though this one now soldered to the scale was found empty. Last time it was charged 5+ years ago.