Here is an excellent application note on the care and feeding of 
Vanadium Pentoxide Lithium rechargeable cells.
They have a number of excellent features - and some very negative ones 
as well. Used properly they appear superb. Applied incorrectly they 
can become expensive junk very quickly.

Discharge current for the VL2020 cell that Bob mentioned should not be 
above 0.2 mA while the cell is above 3v. Charging voltage should be 
strictly controlled at 3.4 V. Higher, it dies. Lower, it doesn't fully 
charge. And they are costly.

Against these finnicky specs there is the superb 2% per year self 
discharge rate. This implies a 50 year shelf life - unlikely to be 
true BUT should be in excess of the 10 years or so of many other 
Lithiums.

    http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_Lithium_VL.pdf

The VL3032 rated at 100 mAh provides about 11 uA-years of capacity.
You'd have to be drawing very little current to make use of any 
lifetime over 10 years. At those levels some sort of solar or thermal 
cell may be a better alternative.


        RM 

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