hi there,
i bought a new FP3 battery quite a while ago but ended up not using it yet. I wonder for how long I can store it without opening or using it before it degrades (too much). Or how fast it degrades? Or how bad it gets after how much time?
looking forward to get some clarity on this one 
erik
If you buy the battery, it’s not fully charged. I cannot specify a total life span, but as long as you don’t store the battery fully charged or nearly depleted, you’re good for a couple of years without too much degradation.
Remember to fully charge the battery before you start using it.
And if you decide you want to put your battery to ‘long term storage’ (so you switch to using another one), make sure it’s already partly depleted, like between 65 and 80%.
There’s bound to be technical articles on this, but this is how I do it myself (after reading loads of stuff about Li-Ion batteries).
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Here is some read:
https://batteryuniversity.com/article/bu-702-how-to-store-batteries
They also have plenty more background information, just don’t drown in reading 
I never kept my lithiums off-grid for more than 1 year intentionally (alas didn’t keep measurements) but judging from my unintentionally forgotten batteries even 2 years should be safe (after 1-2 cycles they seemed good as before, ie over 90% capacity).
PS: Their information often seems lengthy and convoluted but I deem them quite reliable.
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Thanks so much for both your contributions!
So maybe some missing data would be at which percentage Fairphone ships new batteries and how long they stay stored before being sold… ?
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There’s also this of course, straight from https://support.fairphone.com/hc/en-us/articles/10380972881681 :
Long-term storage
If your battery/device is fully discharged for a long time, it may require up to 20 minutes of charging before the device can power. If you still can’t power on the device after a couple of hours, the battery might not work anymore.
If you store your battery/device for an extended period, keep it at room temperature, and make sure to charge your battery between 50% and 80% every couple of months.
A fully discharged battery could fall into an over-discharged state. This will severely diminish its capacity to hold a charge.
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Interesting find, I wonder how FP came up with that, when everywhere else it says:
Lower charge of 40-60% (about 3.7-3.8V respectively, not sure), as for temperature the lower the better (even minus -10 seems okay).
Oh well, at least on regular checking I can agree with Fairphone, don’t let it drop below 3.5V.
And in a dry and fire-safe place, of course! (keeping mine in metal cash box when not in use)
Don’t want to scare anyone but here’s a blog from german insurance companies, works well with google translate but even the pictures alone tell you a lot:
https://www.ifs-ev.org/beitraege/?kategorie=32
Take good care of your batteries and slaap lekker