Has anyone measured how much a cell degrades over time, even if they're not being used? There are some studies on batteryuniversity / cadex about this but I wonder if anyone has done so on their n900's -- is it worth stockpiling batteries despite them being perishable?

The cell I'm currently using (an authentic Nokia BL-5J) has LMD of 1029mAh (bq27200.sh) or 1080mAh (bnf), it's got about 2.5 years of use on it as it's been used in my Nokia 5230 before I stared using it in my N900. I think I may need to get a new one sometime - but I wonder if the cells on the market have not been made for years, they must be NOS and likely we're buying these now?