Thanks for helping me to find the relevant figures in the datasheet!
BTW: I have to correct my measurement figures somewhat:
1) With a longer measurement period I saw that current consumption is on average 29..30 uA. When my calculations are correct that would mean for a new CR2032 (235 mAh) a lifetime of about 8000 hours, almost a year. I don't think I will leave the Teensy unpowered for such a long time!
(2) When I power-off the Teensy the 'charging' current is starting at about -0.25uA, but pretty soon going to zero.
Regards, Rob.