Battery Deterioration

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"Rated" Cycles

Remember! Manufacturer "rated cycles" are attainable only if you follow the "recommended" factors. If you do read the manufactures specs you will likely be dismayed at the difference between the maximum and, in small print, the recommended.

Perhaps most noticeable is the disparity in high drain RC airplane Li-Po ... the 2-3 hundred "rated" cycles providing 2-3 dozen usable cycles!

More common is SLA (Sealed Lead Acid) batteries. Rated at say 10Ah and 3-4 hundred cycles. Actual eBike use will take advantage of barely 5-6Ah and, if lucky, a few dozen good quality cycles. See - Batteries LeadAcid


Baseline Cycle Life

Battery Deterioration is due, or assignable, to various factors.

Every other factor is a contributory factor, increasing or decreasing the baseline number of "usable cycles".

Increasing vs Decreasing "Usable Cycles" - Factors

Charge level

'How to Prolong Lithium-based Batteries - Battery University' - batteryuniversity com learn article how to prolong lithium based batteries.jpg

After ~100 cycles, 4.1V might be providing more usable capacity than the 4.3V charged cells!!!

Lithium2.jpg

Discharge Rate

Higher discharge & charge rates greatly degrade battery capacity and usable life

Cycle life and rate.gif


Discharge rate as sole variable

Cycle Life vs Discharge Rate.jpg

Panasonic large 20700 cells at 2C vs 3C discharge rate

Panasonic NCR20700A 2c vs 3c.png

Depth of discharge

Worse! - while charging .1V higher might give 10% more capacity ...

Discharging .1V lower might contribute a meager 2-3% additional capacity!

Capacity Map2.jpg

Logically ... using that additional 2-3% of discharge might cut usable cycles by half ... ?

So, optimally, best performance would be attained by limiting charge-discharge to the central ,capacity bulge, region of battery capacity.

Above graph is for a specific formulation-build of lithium cobalt cell. It should not be considered universally representative.

See - 4.2V vs 4.15V vs 4.1V Li-ion Peak Charge

Capacity Profile - Why?

Lithiums - mAh/100th V - Discharge Tests

Low Tech Capacity Mapping

Temperature

Charge rate

Higher charge rates produce additional heat and amplifies the possibility-danger of overcharge etc.

Accelerating Battery Deterioration - 18650 laptop type LiCo cells exampled

Cell capabilities, discharge-charge rates are closely tied to actual capacity, rather than new rated capacity.

The recommended noted as for best-maximum life.

*40A actual capacity battery

*When capacity degrades to 30A

*When capacity degrades to 20A

*When capacity degrades to 10A

Coping?

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