After reporting the failure of my Miady 16 AH battery (lightly used less than 3 years old), I dug out my “backup” battery: a 9.6 AH K2 Energy battery, purchased in mid 2011. That battery is 12 years old. It had not been recharged since December of 2021 (2.5 years ago).
I used my battery analyzer to do a simple constant current discharge and found the battery had a capacity of 8.7 AH, even after self-discharging for 2.5 years.
So there is clearly a difference between a quality LiFePO4 and a cheap one.
