[Touch Pro, Fuze ROM Development] bauerpavel:
Updated and simplified version here : http://xdaforums.com/showthread.php?p=3846897#post3846897

I've been around this forum for some time now and I have noticed one thing that is spelled in all sub-forums: BATTERY LIFE

So I thought of pulling some info together that is relevant to our Raphs (Li-ion batteries), taken from www.batteryuniversity.com.

Hope you find it helpful and understand better behaviour of your battery :)

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About the Author

Isidor Buchmann is the founder and CEO of Cadex Electronics Inc., in Vancouver BC.

Mr. Buchmann has a background in radio communications and has studied the behavior of rechargeable batteries in practical, everyday applications for two decades. Award winning author of many articles and books on batteries, Mr. Buchmann has delivered technical papers around the world.

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"If possible, do not discharge lithium-based batteries too deeply. Instead, recharge more often."

Lithium-ion

is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery's life. In addition, the self-discharge is less than half compared to nickel-cadmium, making lithium-ion well suited for modern fuel gauge applications.

Charging

There is only one way to charge lithium-based batteries. The so-called 'miracle chargers', which claim to restore and prolong batteries, do not exist for lithium chemistries. Neither does super-fast charging apply. Manufacturers of lithium-ion cells have very strict guidelines in charge procedures and the pack should be charged as per the manufacturers "typical" charge technique.

Lithium-ion is a very clean system and does not need priming as nickel-based batteries do. The 1st charge is no different to the 5th or the 50th charge. Stickers instructing to charge the battery for 8 hours or more for the first time may be a leftover from the nickel battery days.

Most cells are charged to 4.20 volts with a tolerance of +/?0.05V/cell. Charging only to 4.10V reduced the capacity by 10% but provides a longer service life. Newer cell are capable of delivering a good cycle count with a charge to 4.20 volts per cell.

A lithium-ion battery provides 300-500 discharge/charge cycles. The battery prefers a partial rather than a full discharge. Frequent full discharges should be avoided when possible. Instead, charge the battery more often or use a larger battery. There is no concern of memory when applying unscheduled charges.

Batteries live longer if treated in a gentle manner. High charge voltages, excessive charge rate and extreme load conditions have a negative effect on battery life. The longevity is often a direct result of the environmental stresses applied. The following guidelines suggest ways to prolong battery life.

The time at which the battery stays at 4.20/cell should be as short as possible. Prolonged high voltage promotes corrosion, especially at elevated temperatures. Spinel is less sensitive to high voltage.

The lower charge current reduces the time in which the cell resides at 4.20V. A 0.5C charge only adds marginally to the charge time over 1C because the topping charge will be shorter. A high current charge tends to push the voltage into voltage limit prematurely.

Do not discharge lithium-ion too deeply. Instead, charge it frequently. Lithium-ion does not have memory problems like nickel-cadmium batteries. No deep discharges are needed for conditioning.

Do not charge lithium-ion at or below freezing temperature. Although accepting charge, an irreversible plating of metallic lithium will occur that compromises the safety of the pack.

Not only does a lithium-ion battery live longer with a slower charge rate; moderate discharge rates also helps.

Discharge of the lithium-ion battery is 5% in the first 24 hours after charge, and then reduces to 1% to 2% per month thereafter. The safety circuit adds about 3%. High cycle count and aging have little effect on the self-discharge of lithium-based batteries.

The battery industry is making incremental capacity gains of 8-10% per year. This trend is expected to continue. This, however, is a far cry from Moore's Law that specifies a doubling of transistors on a chip every 18 to 24 months. Translating this increase to a battery would mean a doubling of capacity every two years. Instead of two years, lithium-ion has doubled its energy capacity in 10 years.

Although lithium-ion is memory-free in terms of performance deterioration, batteries with fuel gauges exhibit what engineers refer to as "digital memory". Here is the reason: Short discharges with subsequent recharges do not provide the periodic calibration needed to synchronize the fuel gauge with the battery's state-of-charge. A deliberate

full discharge and recharge every 30 charges

corrects this problem. Letting the battery run down to the cut-off point in the equipment will do this. If ignored, the fuel gauge will become increasingly less accurate.

Despite its overall advantages, lithium-ion has its drawbacks. It is fragile and requires a protection circuit to maintain safe operation. Built into each pack, the protection circuit limits the peak voltage of each cell during charge and prevents the cell voltage from dropping too low on discharge. In addition, the cell temperature is monitored to prevent temperature extremes. The maximum charge and discharge current on most packs are is limited to between 1C and 2C. With these precautions in place, the possibility of metallic lithium plating occurring due to overcharge is virtually eliminated.

The worst condition is keeping a fully charged battery at elevated temperatures, which is the case with running laptop batteries. If used on main power, the battery inside a laptop will only last for 12-18 months. I must hasten to explain that the pack does not die suddenly but begins with reduced run-times.

The voltage level to which the cells are charged also plays an important role to longevity. For safety reasons, most lithium-ion cannot exceed 4.20 volts per cell. While a higher voltage boosts capacity, the disadvantage is lower cycle life.

"how deep can a battery be discharged and still achieve maximum service life?" There are no definite answers. Batteries are like us humans. Suppose we ate all the vegetables our mother heaped on our plates and do our daily exercise, would we life longer? Perhaps. But by how much, no one will know. Batteries lose capacity as part of aging, cycling and exposure to heat. Nickel-cadmium also loses capacity due to lack of exercise because of memory.

Some lithium-ion batteries fail due to excessive low discharge. If discharged below 2.5 volts per cell, the internal safety circuit opens and the battery appears dead.

Aging

is a concern with most lithium-ion batteries and many manufacturers remain silent about this issue. Some capacity deterioration is noticeable after one year, whether the battery is in use or not.

Lithium-ion batteries lose capacity through cell oxidation, a process that occurs naturally during use and aging. The typical life span of lithium-ion is 2-3 years under normal use. Cool storage a 40% charge minimizes aging. An aged lithium-ion cannot be restored with cycling.

Shorted Cells

Manufacturers are often unable to explain why some cells develop high electrical leakage or an electrical short while still relatively new. The suspected culprit is foreign particles that contaminate the cells during manufacturing.

Cell reversal caused by deep discharging also contributes to shorted cells.Specified to deliver 100% capacity when new, the battery should be replaced when the capacity drops to below 80% of the nominal rating.

The self-discharge on all battery chemistries increase at higher temperatures. Typically, the rate doubles with every 10°C (18°F). A noticeable energy loss occurs if a battery is left in a hot vehicle.

Premature voltage cut-off

Not all stored battery power can be fully utilized. Some equipment cuts off before the designated end-of-discharge voltage is reached and precious battery energy remains unused. Applications demanding high current bursts push the battery voltage to an early cut-off. This is especially visible on batteries with elevated internal resistance. The voltage recovers when the load is removed and the battery appears normal. Discharging such a battery on a moderate load with a battery analyzer to the respective end-of-discharge threshold will sometimes produce residual capacity readings of 30% and higher.