Micrel, Inc.

MIC79110

October 2007

9

M9999-102507

All lithium-ion batteries take approximately 3 hours to

charge with the second stage taking twice as long as the

first stage. Some chargers claim to be fast chargers by

skipping the second stage and just charges the battery

until the cell voltage is reached. This only charges the

battery to 70% capacity.

An increase in the charge current during stage 1 does

not shorten the total charge time. It will only shorten the

time for stage 1 to complete and lengthen the time in

stage 2.

The lithium-ion loses charge due to aging whether it is

used or not. Do not store the batteries at full charge and

high heat because it will accelerate the aging process.

Try and store with 40% charge and in a cool

environment.

Lithium-Ion Safety Precautions

Every lithium-ion battery pack should have a safety

circuit which monitors the charge and discharge of the

pack and prevents dangerous occurrences. The

specifications of these safety circuits are dictated by the

cell manufacturer and may include the following:

•

Reverse polarity protection

•

Charge temperature must not be charged when

temperature is lower than 0°C or above 45°C.

•

Charge current must not be too high, typically below

0.7°C

•

Discharge current protection to prevent damage due

to short circuits.

•

Protection circuitry for over voltage applied to the

battery terminals.

•

Overcharge protection circuitry to stop charge when

the voltage per cell rises above 4.3V.

•

Over discharge protection circuitry to stop discharge

when the battery voltage falls below 2.3V (varies

with manufacturer).

•

Thermal shutdown protection for the battery if the

ambient temperature is above 100°C.