In the meantime the life of Lithium batteries is greatly extended by not letting then deeply discharge or get overly warm or cold.

Even in storage out of a device the internal safety circuit draws current to monitor the battery voltage which causes self discharge and if the voltage drops below the safe point then for safety the battery is terminated and cannot be recharged. So just don't leave them lying around or in devices, which nowadays do not seem to have a physical on/off switch so always draw current, and recharge them at least two or three times a year if they are not in a daily use cycle.

That Jolla has a user replaceable battery is a brilliant Unique Selling Point and a great feature for those who like to visit remote places.

Also remove the battery and neither the MNO or state security will know where you are until you repower your phone

Richard