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January 22, 2006, 7:00 am
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Battery research is focusing heavily on lithium chemistries, so much
so that one could presume that all portable devices will be powered
with lithium-ion batteries in the future. In many ways, lithium-ion is
superior to nickel and lead-based chemistries and the applications for
lithium-ion batteries are growing as a result.
Lithium-ion has not yet fully matured and is being improved
continuously. New metal and chemical combinations are being tried
every six months to increase energy density and prolong service life.
The improvements in longevity after each change will not be known for
a few years.
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.
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. (Read more in 'Choosing the right battery
for portable computing', Part Two.)
Aging of lithium-ion is an issue that is often ignored. A lithium-ion
battery in use typically lasts between 2-3 years. The capacity loss
manifests itself in increased internal resistance caused by oxidation.
Eventually, the cell resistance reaches a point where the pack can no
longer deliver the stored energy although the battery may still have
ample charge. For this reason, an aged battery can be kept longer in
applications that draw low current as opposed to a function that
demands heavy loads. Increasing internal resistance with cycle life
and age is typical for cobalt-based lithium-ion, a system that is used
for cell phones, cameras and laptops because of high energy density.
The lower energy dense manganese-based lithium-ion, also known as
spinel, maintains the internal resistance through its life but loses
capacity due to chemical decompositions. Spinel is primarily used for
The speed by which lithium-ion ages is governed by temperature and
state-of-charge. Figure 1 illustrates the capacity loss as a function
of these two parameters.
Figure 1: Permanent capacity loss of lithium-ion as a function of
temperature and charge level.
High charge levels and elevated temperatures hasten permanent capacity
loss. Improvements in chemistry have increased the storage performance
of lithium-ion batteries.
The mentioning of limited service life on lithium-ion has caused
concern in the battery industry and I will need to add some
clarifications. Let me explain:
If someone asks how long we humans live, we would soon find out that
the longevity varies according to life style and living conditions
that exist in different countries. Similar conditions exist with the
batteries, lithium-ion in particular. Since BatteryUniversity bases
its information on the feedback from users as opposed to scientific
information derived from a research lab, longevity results may differ
from manufacturer' specifications. Let's briefly look at the various
living conditions of the lithium-ion battery.
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.
There are no remedies to restore lithium-ion once worn out. A
momentary improvement in performance is noticeable when heating up the
battery. This lowers the internal resistance momentarily but the
condition reverts back to its former state when the temperature drops.
Cold temperature will increase the internal resistance.
If possible, store the battery in a cool place at about a 40%
state-of-charge. Some reserve charge is needed to keep the battery and
its protection circuit operational during prolonged storage. Avoid
keeping the battery at full charge and high temperature. This is the
case when placing a cell phone or spare battery in a hot car. Running
a laptop computer on the mains has a similar temperature problem.
While the battery is kept fully charged, the inside temperature during
operation rises to 45°C (113°F).
Removing the battery from the laptop when running on fixed power
protects the battery from heat but some battery and laptop
manufacturers caution against this practice. They say that dust and
moisture accumulating inside the battery casing could damage the
laptop. There is little evidence of this occurring in an office
The question is often asked, should the laptop be disconnected from
the main when not in use? With lithium-ion it does not matter. Once
the battery is fully charged, no further charge is applied.
All personal computers (and other electronic devices) contain an
embedded battery for memory back up. This battery is commonly a small
non-rechargeable lithium cell, which provides a small current while
the device is turned off. The PC uses the battery to retain the BIOS
settings, date and time, as well as resource assignment for Plug and
Play systems when the power is off. Storing the device unplugged does
shorten the service life of the backup battery to a few years. Some
say 1-2 years. By keeping the computer connected to the main, albeit
turned off, a battery on the PC motherboards should be good for 5-7
years. Most PCs give an advanced warning when battery gets low. A dead
back-up battery will wipe out the volatile memory and erase the
settings. Take your portable device to a service center for the
replacement for the memory back up battery.
A large number of lithium-ion batteries for cell phones are being
discarded under the warranty return policy. Some failed batteries are
sent to service centers or the manufacturer, where they are
refurbished. Studies show that 80%-90% of the returned batteries can
be repaired and returned to service.
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. A charge with the original charger is no
longer possible. Some battery analyzers (Cadex) feature a boost
function that reactivates the protection circuit of a failed battery
and enables a recharge. However, if the cell voltage has fallen below
1.5V/cell and has remained in that state for a few months, a recharge
should be avoided because of safety concerns. To prevent failure,
never store the battery fully discharged. Apply some charge before
storage, and then charge fully before use.
All personal computers (and some other electronic devices) contain a
battery for memory back up. This battery is commonly a small
non-rechargeable lithium cell, which provides a small current when the
device is turned off. The PC uses the battery to retain certain
information when the power is off. These are the BIOS settings,
current date and time, as well as resource assignment for Plug and
Play systems. Storage does shorten the service life of the backup
battery to a few years. Some say 1-2 years. By keeping the computer
connected to the main, albeit turned off, a battery on the PC
motherboards should be good for 5-7 years. A PC should give the
advanced warning when battery gets low. A dead back-up battery will
wipe out the volatile memory and erase certain settings. After battery
is replaced, the PC should again be operational.
* Avoid frequent full discharges because this puts additional
strain on the battery. Several partial discharges with frequent
recharges are better for lithium-ion than one deep one. Recharging a
partially charged lithium-ion does not cause harm because there is no
memory. (In this respect, lithium-ion differs from nickel-based
batteries.) Short battery life in a laptop is mainly cause by heat
rather than charge / discharge patterns.
* Batteries with fuel gauge (laptops) should be calibrated by
applying a deliberate full discharge once every 30 charges. Running
the pack down in the equipment does this. If ignored, the fuel gauge
will become increasingly less accurate and in some cases cut off the
* Keep the lithium-ion battery cool. Avoid a hot car. For
prolonged storage, keep the battery at a 40% charge level.
* Consider removing the battery from a laptop when running on
fixed power. (Some laptop manufacturers are concerned about dust and
moisture accumulating inside the battery casing.)
* Avoid purchasing spare lithium-ion batteries for later use.
Observe manufacturing dates. Do not buy old stock, even if sold at
* If you have a spare lithium-ion battery, use one to the fullest
and keep the other cool by placing it in the refrigerator. Do not
freeze the battery. For best results, store the battery at 40%
Created: February 2003, Last edited: November 2005
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