Li-ion battery life

[jbolland]

One of my bikes is a conversion - the front hub nano motor with 6ah li-on battery. I've had it over a year but used it sparingly - mybe 200miles at most. (Iprefer my wife's kalkhoff agattu).
The battery recently only gives me 5miles or so, and it takes only 1 to1-1/2 hrs to charge fully compared to 4-5hrs when it was normal.
The 3 LEDs stay on right until the end when they all go out - they used to phase out as the power was depleted.
I've checked the battery voltage when charged - it is 41-42V, and when empty is 7-8v.
I've put the bike on a stand and run the battery down from full 3 times but made no difference.
Any ideas anyone.(Yes I know.... stick to the kalkhoff....) It seems a lot of money for a battery which doesn't last the pace and I'm very disappointed.

 

[flecc]

I'm afraid that battery is faulty, it should never drop below 31.5 volts when empty, so clearly it's internal battery management system (if any) hasn't been protecting it. Dropping that low has hastened the cells decline and they cannot be recovered from that. On a well designed nominal 36 volt lithium battery, the BMS will cut the current when the voltage drops to 31.5.

Lithium batteries die with age as well as use, so the low mileage doesn't really indicate anything. Once they've been manufactured the chemical decay starts until the battery reaches end of life, and in the cheaper ones that loss of capacity can be very high, over 35% per annum in some cases. Exactly how fast they decline is set by the conditions of use such as the rates of discharge and the ambient and working temperatures.
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