Hi Bill and
to the forum.
When lithium batteries were first introduced, users were encouraged to keep them fully charged during storage to ensure that the voltage would not drop low enough to cause permanent
(irreversible) damage to the cells.
Over time, the information has changed, and it is now recommended to store batteries in a cool place with a state of charge between 40~50% to reduce the degradation while the pack is not being used.
Storing a pack at 100% state of charge in high temperatures will cause the battery to lose capacity much quicker than storing it at 40% state of charge in a cooler temperature:
Lithium-ion must be stored in a charged state, ideally at 40 percent. This prevents the battery from dropping below 2.50V/cell, triggering sleep mode.
In addition to the storage degradation, the number of discharge cycles is also affected by how low the pack is discharged each time it is used:
If you regularly discharge your battery pack until it is completely empty, the number of available cycles can also be reduced.
My questions are:
1. Can those storage temperatures do damage to the battery?
2. Did I damage the battery leaving it at 100% charge state with maintenance charging every ~ 2 – 3 months during those 2 years of inactivity?
3. Last three bike rides I have ran it through as noted to its safe discharge state. Can I restore some of the batteries capacity by “exercising” (Full discharge and recharge) or is the damage permanent?
4. In simpler wording is the battery trashed?
You have probably found the answers already, but my answers are:
1. Yes, but higher temperatures would have caused even more damage/degradation.
2. Yes, storing it with a lower state of charge would have reduced the damage/degradation.
3. It may recover slightly, but I suspect the damage/degradation is likely be permanent.
4. I wouldn't say it is trashed, it simply has a much lower usable capacity now than it did before the 2 years of storage.
(25~27km of range is a lot better than a battery that doesn't work at all.) Alan