Originally Posted by Mono
Quote from Wiki:
"A Standard (Cobalt) Li-ion cell that is full most of the time at 25 °C (77 °F) irreversibly loses approximately 20% capacity per year. Poor ventilation may increase temperatures, further shortening battery life. Loss rates vary by temperature: 6% loss at 0 °C (32 °F), 20% at 25 °C (77 °F), and 35% at 40 °C (104 °F). When stored at 40%–60% charge level, the capacity loss is reduced to 2%, 4%, and 15%, respectively. In contrast, the calendar life of LiFePO4 cells is not affected by being kept at a high state of charge
So, it battery is full and is stored at room temperature, it has no capacity in 5 years, even if not used. To keep it in good health possibly requires it to store it half-charged and in refrigerator.
But, there is not only one type of Li-ion battery, but about 5+. The citation holds for standard one....
M92 is not comparable to cell-phone. Modern cell phone has to be charged every 1-5 days (depending if smart or not). M92 say every 2 weeks... Depends if WiFi is used... So it may be 25 charging cycles per year comparing to 360 cycles/yr for smarphone.
So the upshot is: in order to avoid battery capacity degradation charge it once every say six months and store it in the fridge. Works for me and I'd prefer it from not been able to find a spare battery, specially if the battery is only 10 €.