What Is The Energizer 'ultimate Lithium' Aa Cell Actual Failure Rate?

I switched to Energizer Ultimate Lithium leak-proof AA cells for all my emergency equipment that uses AA cells (lighting, radio receivers, etc.). Energizer says that these cells still have at least 50% of their considerable original capacity 20 years after the date of manufacture, and they never leak. That's a big claim. However, after 7 years, I've had several such cells die an early death without ever being used, and two have leaked out their electrolyte, resulting in damage to the device they were installed in. None of the devices have any parasitic current drain, as they are designed to be stored until needed in an emergency.I'm seeking test data that will tell me the type of failure and expected failure rates of these cells in various storage conditions. Of great importance is how long the cells can truly be stored without any cells failing or leaking. These cells very clearly do not perform as promised, but how well do they perform, especially when compared to other cells and cell chemistries (e.g. Duracell alkaline)?