Envelope of ....
My phone has a 2 day + battery allowing me only charge to, most days, use a safe envelope of a 75 / 35 or 80 / 35 charge regime.
Even in 10 years time, the low degradation of safe charging should mean things are still A1 with regards to the internal consumable.
No needs to pass a stuffed brown envelope for me. 1 day fast fail batteries are simply not acceptable.