Aging is a concern with most lithium-ion batteries. Some capacity
deterioration is noticeable after one year, whether the battery is in
use or not. The battery frequently fails after two or three years.
Storage in a cool place slows the aging process of lithium-ion.
Manufacturers recommend storage temperatures of 15°C (59°F). In
addition, the battery should be partially charged during storage. The
manufacturer recommends a 40% charge.
An increase of the internal resistance occurs with cycling and aging.
After 2-3 years of use, the pack often becomes unserviceable due to a
large voltage drop under load that is caused by high internal
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.
Not only does a lithium-ion battery live longer with a slower charge
rate; moderate discharge rates also help. Shown below the cycle life as a
function of charge and discharge rates. Observe the improved laboratory
performance on a charge and discharge rate of 1C compared to 2 and 3C.
A moderate charge and discharge puts less stress on the battery,
resulting in a longer cycle life.
Battery experts agree that the longevity of lithium-ion is shortened
by other factors than charge and discharge rates. Even though
incremental improvements can be achieved with careful use, our
environment and the services required are not always conducive for
optimal battery life. In this respect, the battery behaves much like us
humans - we cannot always live a life that caters to achieve maximum
Limit the time at which the battery stays at 4.20V/cell. Prolonged
high voltage promotes corrosion, especially at elevated temperatures.
3.92V/cell is the best upper voltage threshold for cobalt-based
lithium-ion. Charging batteries to this voltage level has been shown to
double cycle life. Lithium-ion systems for defense applications make use
of the lower voltage threshold. The negative is reduced capacity.
The charge current of Li-ion should be moderate (0.5C for
The lower charge current reduces the time in which the cell resides
at 4.20V. It should be noted that 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 up and forces it into the
voltage limit prematurely.
Lithium-ion works within the discharge temperature limits of -20°C to
60°C (-4°F to 140°F). The performance is temperature based, meaning
that the rate capability at or below -20°C is reduced due to the
increased impedance of the electrolyte. Discharging at low temperatures
does not harm the battery. Lithium-ion may be used down to -30°C (-22°F)
with acceptable results. Larger packs will be necessary to compensate
for the reduced capacity at these temperatures.
It is not recommended to discharge lithium-ion at temperatures above
60°C. High discharge rates combined with elevated temperatures can cause
self-heating, an effect that could permanently damage the separator and
electrodes of the cells.
One of the urgent requirements of a battery for digital applications
is low internal resistance. Measured in milliohms, the internal
resistance is the gatekeeper that, to a large extent, determines the
runtime. The lower the resistance, the less restriction the battery
encounters in delivering the needed power spikes. A high mW reading can
trigger an early 'low battery' indication on a seemingly good battery
because the available energy cannot be delivered in the required manner
and remains in the battery.