MarkT:
lithium coin cells (as used in calculators) are good for about 1 or 2mA only, they will deliver more
with voltage dropping considerably (for instance they can power an LED as the voltage just falls
to the forward voltage of the LED before the current gets anything like large).
The Li-Ion LIR2032 can handle much higher current. About 17mA constant and up to 75mA pulsed. They have a tiny capacity though.
I've ordered a couple to try out and see how well they do.