There are many factors that affect Li-ion battery life and performance. The main factors are - Charging speed, the DoD (Depth of Discharge), Loading and the exposure to high temperatures.
A Li-ion battery works by the ion movement between the anode & the cathode. While recharging the ions flow back. So you would think that this cycle will go for a long period. However, cycling, aging and temperature effects decrease the battery performance.
The DoD (Depth of Discharge) determines the cycle count of the battery. The smaller the discharge the longer the battery will survive. So avoid full discharging of the battery and make sure that you charge the battery more often between uses.
There is NO memory effect in Li-Ion batteries and hence it does NOT need full discharge cycles at all.
Li-ion batteries are stressed due to heat & high charge voltage. A battery operating above 30 deg C is a high temperature for most Li-ions and a charging voltage above 4.10V/cell is taken as high voltage. These two factors contribute to permanent capacity loss.
Most Li-ions charge to 4.20V/cell, and every reduction in peak charge voltage of 0.10V/cell is said to double the cycle life. A lithium-ion cell charged to 4.20V/cell typically delivers 300–500 cycles. If charged to only 4.10V/cell, the life can be prolonged to 600–1,000 cycles; 4.0V/cell should deliver 1,200–2,000 and 3.90V/cell should provide 2,400–4,000 cycles.
However, it should be noted that a lower peak charge voltage reduces the capacity the battery stores. Every 70mV reduction in charge voltage lowers the overall capacity by 10 percent.
The optimal charge voltage is 3.92V/cell. This gives the longest battery life. Experts believe that this threshold eliminates all voltage-related stresses.
Li-ion used in satellites must also endure a lifespan of 8 years and more. To achieve this, the cells are charged to only 3.90V/cell and lower. An interesting discovery was made by NASA in that Li-ion dwelling above 4.10V/cell tend to decompose due to electrolyte oxidation on the cathode, while those charged to lower voltages lose capacity due to the SEI buildup on the anode.
It's too difficult and time consuming to write everything in a forum and if anyone is interested there is much research done by the University of Halifax and also by another University in Sweden about various Li batteries.
