PRECAUTIONS FOR DESIGNING DEVICES WITH NI-MH BATTERIES

In order to take full advantage of the properties of Ni- 1.3 Reverse charging
MH batteries and also to prevent problems due to • Never attempt reverse charging.
improper use, please note the following points Charging with polarity reversed can cause a
during the use and design of battery operated reversal in battery polarity causing gas pressure
products. inside the battery to rise, which can activate the
safety vent, lead to alkaline electrolyte leakage,
Underlined sections indicate information rapid deterioration in battery performance, battery
that is especially important swelling or battery rupture.

1. Charging 1.4 Overcharging

1.1 Charging temperature • Avoid overcharging. Repeated overcharging can
• Charge batteries within an ambient temperature lead to deterioration in battery performance.
range of 0°C to 40°C. (“Overcharging” means charging a battery when it
• Ambient temperature during charging affects is already fully charged.)
charging efficiency. Since charging efficiency is
1.5 Rapid charging
best within a temperature range of 10°C to
• To charge batteries rapidly, use the specified
30°C, whenever possible, place the charger
charger (or charging method recommended by
(battery pack) in a location that is within this
Panasonic) and follow the correct procedures.
temperature range.
• At temperatures below 0°C the gas absorption 1.6 Trickle charging (continuous charging)
reaction is not adequate, causing gas pressure • Trickle charging cannot be used with Ni-MH batter-
inside the battery to rise, which can activate the ies. However, after applying a refresh charge using
safety vent and lead to leakage of alkaline gas a rapid charge, use a trickle charge of 0.033 CmA
and deterioration in battery performance. to 0.05 CmA.
• Charging efficiency drops at temperatures Also, to avoid overcharging with trickle charge,
above 40°C. This can disrupt full charging and which could damage the cell characteristics, a
lead to deterioration in performance and battery timer measuring the total charge time should be
leakage. used.
• Note : “CmA”
1.2 Parallel charging of batteries During charging and discharging, CmA is a value
• Sufficient care must be taken during the design indicating current and expressed as a multiple of
of the charger when charging batteries nominal capacity. Substitute “C” with the battery’s
connected in parallel. nominal capacity when calculating. For example,
Consult Panasonic when parallel charging is for a 1500mAh battery of 0.033CmA, this value is
required. equal to 1/30 × 1500, or roughly 50mA.

NICKEL METAL HYDRIDE HANDBOOK AUGUST 2003

This information is generally descriptive only and is not intended to make or imply any representation, guarantee or warranty with respect to any cells and batteries. Cell and battery designs/specifications are subject to
modification without notice. Contact Panasonic for the latest information.
PRECAUTIONS FOR DESIGNING DEVICES WITH NI-MH BATTERIES- CONTINUED

2. Discharging 3.2 Long-term storage (1 year, -20°C to +35°C)

2.1 Discharge temperature • Because long-term storage can accelerate
• Discharge batteries within an ambient tempera- battery self-discharge and lead to the deactivation
ture range of -10°C to +45°C. of reactants, locations where the temperature
• Discharge current level (i. e. the current at which ranges between +10°C and +30°C are suitable
a battery is discharged) affects discharging for long-term storage.
efficiency. Discharging efficiency is good within a • When charging for the first time after long-term
current range of 0.1 CmA to 2 CmA. storage, deactivation of reactants may lead to
• Discharge capacity drops at temperatures below increased battery voltage and decreased battery
-10°C or above +45°C. Such decreases in capacity. Restore such batteries to original
discharge capacity can lead to deterioration in performance by repeating several cycles of
battery performance. charging and discharging.
• When storing batteries for more than 1 year,
2.2 Overdischarge (deep discharge) charge at least once a year to prevent leakage
• Since overdischarging (deep discharge) damages and deterioration in performance due to self-
the battery characteristics, do not forget to turn off discharging.
the switch when discharging, and do not leave the
battery connected to the equipment for long 4. Service Life of Batteries
periods of time. Also, avoid shipping the battery 4.1 Cycle life
installed in the equipment. • Batteries used under proper conditions of charg-
ing and discharging can be used 500 cycles or
2.3 High-current discharging more.
• As high-current discharging can lead to heat Significantly reduced service time in spite of
generation and decreased discharging effi- proper charging means that the life of the battery
ciency, consult Panasonic before attempting has been exceeded.
continuous discharging or pulse discharging at Also, at the end of service life, an increase in
currents larger than 2 CmA. internal resistance, or an internal short-circuit
failure may occur. Chargers and charging circuits
3. Storage should therefore be designed to ensure safety in
3.1 Storage temperature and humidity (short-term) the event of heat generated upon battery failure at
• Store batteries in a dry location with low humidity, the end of service life.
no corrosive gases, and at a temperature range
4.2 Service life with long-term use
of -20°C to +45°C.
• Because batteries are chemical products involv-
• Storing batteries in a location where humidity is
ing internal chemical reactions, performance
extremely high or where temperatures fall below -
deteriorates not only with use but also during
20°C or rise above +45°C can lead to the rusting
prolonged storage.
of metallic parts and battery leakage due to
Normally, a battery will last 2 years (or 500
expansion or contraction in parts composed of
cycles) if used under proper conditions and not
organic materials.
overcharged or overdischarged. However, failure
to satisfy conditions concerning charging, dis-
charging, temperature and other factors during
actual use can lead to shortened life (or cycle
life) damage to products and deterioration in
performance due to leakage and shortened
service life.

NICKEL METAL HYDRIDE HANDBOOK AUGUST 2003

This information is generally descriptive only and is not intended to make or imply any representation, guarantee or warranty with respect to any cells and batteries. Cell and battery designs/specifications are subject to
modification without notice. Contact Panasonic for the latest information.
PRECAUTIONS FOR DESIGNING DEVICES WITH NI-MH BATTERIES- CONTINUED

5. Design of Products Which Use Batteries 5.5 Overdischarge (deep discharge) prevention
5.1 Connecting batteries and products • Overdischarging (deep discharging) or reverse
• Never solder a lead wire and other connecting charging damages the battery characteristics. In
materials directly to the battery, as doing so will order to prevent damage associated with forget-
damage the battery’s internal safety vent, separa- ting to turn off the switch or leaving the battery in
tor, and other parts made of organic materials. the equipment for extended periods, preventative
To connect a battery to a product, spot-weld a tab options should be incorporated in the equipment.
made of nickel or nickel-plated steel to the At the same time, it is recommended that leak-
battery’s terminal strip, then solder a lead wire to age current is minimized. Also, the battery should
the tab. not be shipped inside the equipment.
Perform soldering in as short a time as possible.
• Use caution in applying pressure to the terminals
in cases where the battery pack can be sepa-
rated from the equipment.

5.2 Material for terminals in products using the

batteries
• Because small amounts of alkaline electrolyte
can leak from the battery seal during extended
use or when the safety vent is activated during
improper use, a highly alkaline-resistant material
should be used for a product’s contact terminals
in order to avoid problems due to corrosion.
High Alkaline-resistant Metals Low Alkaline-resistant Metals
Nickel, stainless steel, nickel- Tin, aluminum, zinc, copper, brass,
plated steel, etc. etc.
(Note that stainless steel generally results in higher contact resistance.)

5.3 Temperature related the position of batteries in

products
• Excessively high temperatures (i.e. higher than
45°C) can cause alkaline electrolyte to leak from
the battery, thus damaging the product and
shorten battery life by causing deterioration in the
separator or other battery parts. Install batteries
far from heat-generating parts of the product.
The best battery position is in a battery compart-
ment that is composed of an alkaline-resistant
material which isolates the batteries from the
product’s circuitry. This prevents damage that
may be caused by a slight leakage of alkaline
electrolyte from the battery.

5.4 Discharge end voltage

• The discharge end voltage is determined by the
formula given below. Please set the end voltage
of each battery at 1.1 volts or less.

Number of Batteries Arranged Serially

1 to 6 (Number of batteries x 1.0) V
7 to 12 ((Number of batteries - 1) x 1.2) V

NICKEL METAL HYDRIDE HANDBOOK AUGUST 2003

This information is generally descriptive only and is not intended to make or imply any representation, guarantee or warranty with respect to any cells and batteries. Cell and battery designs/specifications are subject to
modification without notice. Contact Panasonic for the latest information.
PRECAUTIONS FOR DESIGNING DEVICES WITH NI-MH BATTERIES- CONTINUED

6. Prohibited Items Regarding the Battery 6.7 Installation in equipment (with an airtight battery
Handling compartment)
• Panasonic assumes no responsibility for prob- • Always avoid designing airtight battery compart-
lems resulting from batteries handled in the ments. In some cases, gases (oxygen, hydro-
following manner. gen) may be given off, and there is a danger of
the batteries bursting or rupturing in the presence
6.1 Disassembly of a source of ignition_(sparks generated by a
Never disassemble a battery, as the electrolyte motor switch, etc.).
inside is strong alkaline and can damage skin and
clothes. 6.8 Use of batteries for other purposes
• Do not use a battery in an appliance or purpose
6.2 Short-circuiting for which it was not intended. Differences in
Never attempt to short-circuit a battery. Doing so specifications can damage the battery or appli-
can damage the product and generate heat that ance.
can cause burns.
6.9 Short-circuiting of battery packs
6.3 Throwing batteries into a fire or water • Special caution is required to prevent short-
Disposing of a battery in fire can cause the circuits.
battery to rupture. Also avoid placing batteries in Care must be taken during the design of the
water, as this causes batteries to cease to battery pack shape to ensure batteries cannot be
function. inserted in reverse. Also, caution must be given
to certain structures or product terminal shapes
6.4 Soldering which can make short-circuiting more likely.
Never solder anything directly to a battery. This
can destroy the safety features of the battery by 6.10 Using old and new batteries together
damaging the safety vent inside the cap. • Avoid using old and new batteries together. Also
avoid using these batteries with ordinary dry-cell
6.5 Inserting the batteries with their polarities re- batteries, Ni-Cd batteries or with another
versed manufacturer’s batteries.
Never insert a battery with the positive and nega- Differences in various characteristic values, etc.,
tive poles reversed. as this can cause the battery can cause damage to batteries or the product.
to swell or rupture.
7. Other Precautions
6.6 Overcharging at high currents and reverse • Batteries should always be charged prior to use.
charging Be sure to charge correctly.
• Never reverse charge or overcharge with high
currents (i.e. higher than rated). Doing so causes 8. Final Point to Bear in Mind
rapid gas generation and increased gas pressure, • In order to ensure safe battery use and to prolong
thus causing batteries to swell or rupture. the battery performance, please consult
• Charging with an unspecified charger or specified Panasonic regarding charge and discharge
charger that has been modified can cause batter- conditions for use and product design prior to the
ies to swell or rupture. Be sure to indicate this release of a battery-operated product.
safety warning clearly in all operating instructions
as a handling restriction for ensuring safety.

NICKEL METAL HYDRIDE HANDBOOK AUGUST 2003

This information is generally descriptive only and is not intended to make or imply any representation, guarantee or warranty with respect to any cells and batteries. Cell and battery designs/specifications are subject to
modification without notice. Contact Panasonic for the latest information.