> I don't know why you are fixed on 1.6V.

It's not me - it's the circuit !!!

The optimum V range is 1.55V to 1.65V, so I figured to
keep some overhead for longevity, aim for >1.6V

> If you use a lithium coin cell you will have enough headroom
> to put in a double diode in SOT23 to both drop the voltage

All I have to hand for testing is a 3.25V Li cell and some
1N4148s. At the current I require (which btw I erroneously
said was 85pA, it's actually 85nA), each 1N4148 drops
0.4V, so 4 in series would do the job. My meter has a
resolution of 0.001mA +/- 1 digit, so I can't tell what current
the diodes are using. The specs say the reverse current at
20C is 25nA, but I don't know enough about diode data to
say whether those 4 diodes are consuming 100nA. If they
are, then that has implications for the cell. If anyone knows
what current (if any) a 1N4148 uses at 85nA through-current
I'd like to know

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