FAQ

The quantity of electricity that can be obtained from a battery in one
cycle from full charge to full discharge when the battery is discharged under
conditions of rated current level and ambient temperature within the
predetermined range.Generally, capacity is expressed in units of mAh
(milliampere-hour).

a. What is Nominal Capacity?

The standard capacity designated by a battery manufacturer to identify a
particular cell model.

b. What is Nominal Voltage?

The standard voltage used to express the capacity of a particular battery
model. It is generally equal to its electromotive force or its approximate
voltage during normal operation. Typical Values:

o 1.2 volts per cell for NiCd and NiMH

o 3.6 or 3.7 volts per cell for Lithium Ion or Lithium Polymer

o 3 volts per cell for lithium primary

o 2 volts per cell for sealed lead acid

o 1.5 volts per cell for alkaline and carbon zinc .

c. What is discharge rate?

The discharge rate is the rate at which current is removed from a battery.

When a battery is discharged at a current level “i”, for a period until the end
discharge voltage is ‘”h”, the discharge is referred to as the h-hour rate
discharge, while “i” is known as the h-hour rate discharge current. For
practical use, nominal capacity is used as standard.

d. What is End-Voltage ?

The voltage that indicates the end limit of discharge. This voltage is
almost equivalent to limitation of practical use. Typical values:

o 1.0 volt per cell for NiCd and NiMH

o 1.75 volts per cell for sealed lead acid

o 2.75 volts per cell for lithium ion and lithium polymer

o 2.0 volts per cell for primary lithium

o 0.9 volts per cell for alkaline and carbon zinc

e. What is Open circuit voltage ?

The voltage between terminals of a battery without any load.

What is Operating voltage ?

The voltage between terminals when a battery is subjected to a load. Usually

expressed by the voltage of the battery at 50% discharge point.

f. What is Polarity Reversal ?

Reversing of polarity of the terminals of a small-capacity cell in a multi-
cell battery due to overdischarge.

g. What is Positive Electrode ?

The electrode which has a positive potential. Electric current from this
electrode flows in the external circuit during discharge.

h. What is Negative Electrode ?

The plate which has an electrical potential lower than that of the other
plate during normal cell operation. Electric current from the external circuit
flows into the cell at the negative electrode during discharge. Also called
minus electrode.

i. What is Self-Discharge ?

A decrease in battery capacity which occurs without any current flow to an
external circuit. Typical values:

0 ~ 1% per day for NiCd

0 ~ 2% per day for NiMH

0 ~ 0% per day for Lithium Ion and Lithium Polymer .

j. What is Short Circuit ?

Directly connecting the positive electrode (terminal) to the negative
electrode (terminal) of the battery.

k. What is Thermistor ?

A circuit element with a negative temperature coefficient. It is built into
batteries and used to detect ambient temperature or battery temperature. A
battery charger may use this device to properly charge a battery.

l. Resistance of the battery ?

One battery that does not perform well at a 1C discharge rate is the
portable sealed lead-acid. To obtain a reasonably good capacity reading,
manufacturers commonly rate these batteries at 0.05C or 20 hour discharge. Even
at this slow discharge rate, a 100% capacity is hard to attain. To compensate
for different readings at various discharge currents, manufacturers offer a
capacity offset. Applying the offset to correct the capacity readout does not
improve battery performance; it merely adjusts the capacity calculation if
discharged at a higher or lower C-rate than specified.
Lithium-ion/polymer batteries are electronically protected against high load
currents. Depending on battery type, the discharge is limited to between 1C and
2C. This protection makes the lithium ion unsuitable for biomedical equipment
and power tools demanding high inrush currents.

2. What’s the best battery for laptops?

Batteries for laptops have a unique challenge - they must be small and
lightweight.In fact, the laptop battery should be invisible to the user and
deliver enough power to endure a five-hour flight from Toronto to Vancouver. In
reality, a typical laptop battery provides only about 90 minutes of service.

Many users complain of much shorter runtimes.

Computer manufacturers are hesitant to add a larger battery because of
increased size and weight. A recent survey indicated that, given the option of
larger size and more weight for longer runtimes, most users would settle for
what is being offered today. For better or worse, we have learned to accept the
short runtime of a laptop.

The energy density of modern batteries improves by about 10% per year.
However, the benefit of better battery performance is eaten up by higher power
requirements of laptops. This results in the same runtime but more powerful
laptops.

During the last few years, batteries have improved in terms of energy
density. But any benefit in better battery performance is being eaten up by the
higher power requirements of the laptops. This trend is continuing and the net
effect will be the same runtimes but more powerful laptops.
Most laptops are powered by lithium-ion. This chemistry has a high energy
density and is lightweight. There is no immediate breakthrough on the horizon of
a miracle battery that would provide more power than the current electro-
chemical battery.
Fuel cells, when available, will offer a continued stream of power by
allowing the exchange of fuel cartridges when empty. Unfortunately, commercial
fuel cells for laptops and other portable devices are still several years away.
Power handling, size and cost remain the biggest hurdles. The early fuel cells
will function more like a portable charger than a battery replacement. The fuel
cells currently in use have the difficulty in providing spontaneous high power
on demand.
The runtime of a laptop battery is based on the activity of the computer.
The basic housekeeping, which the computer needs to stay alive, draws less power
than, for example, reading, writing, computations and searching for files.
Manufacturers prefer using idle time when specifying runtime.
A battery in a laptop ages more quickly than in other applications because
of heat.During use, the inside temperature of a laptop rises to 45¡?C (113¡?F).
The combination of high temperature and full state-of-charge promotes cell
oxidation, a condition that cannot be reversedonce present. The battery’s life
expectancy when operating at high temperature is half compared to running at a
more moderate 20¡?C (68¡?F) or lower. Leaving the laptop in a parked car under
the hot sun will also aggravate the situation. All batteries suffer permanent
capacity loss as part of elevated temperatures but lithium-ion is affected more
than other batteries.

Some Japanese computer manufacturers have introduced a number of sub-
housing. This design improves battery life because the battery is kept at room
temperature. Some models carry several size batteries to accommodate different
user demands.

Lithium-ion is well suited for laptop users who continually switch from

fixed power to battery use. This user pattern is typical for those in the sales,

service and medical field. Here is the reason why:

With nickel-based batteries, the charger applies a full charge each time the
portable device is connected to fixed power. The battery is put on charge until
a signal is received indicating that the battery is full. This signal is in form
of a voltage change or rising temperature. Because of the sluggish response,
permanent capacity loss occurs caused by overcharge and elevated temperature.
Lithium-ion only receives charge if the voltage is low .

3. How to calibrate the battery?

Most laptop batteries are ’smart’; meaning that they know how much energy is
left.Such a feature has definite benefits but the readings are often
inaccurate. A laptop may indicate 30 minutes of remaining runtime when suddenly
the screen goes dark.Here is the reason why:
With use and time, a tracking error occurs between the chemical battery and
the digital sensing circuit. The most ideal use of the ’smart’ battery, as far
as fuel-gauge accuracy is concerned, is a full charge followed by a full
discharge at a constant current. In such a case, the tracking error would be
less than 1% per cycle. In real life, however, a battery may be discharged for
only a few minutes and the load may vary widely. Long storage also contributes
to errors because the circuit cannot accurately compensate for self-discharge.
Eventually, the true capacity of the battery no longer synchronizes with the
fuel gauge and a deliberate full charge and discharge is needed to ‘re-learn’ or
calibrate the battery.
What happens if no battery calibration is done? Can such a battery be used
in confidence? Most ’smart’ battery chargers obey the dictates of the chemical
cells rather than the electronic circuit. In this case, the battery will fully
charge regardless of the fuel gauge setting and function normally, but the
digital readout will become increasingly more inaccurate. If not corrected, the
fuel gauge simply becomes a nuisance.
At what point of a discharge does the reset occur? Lithium-ion is considered
fully discharged between 2.5 and 3.0 volts per cell. The electronic circuit in
the battery is designed to reset between these voltage levels. A problem occurs
if the laptop cuts off before this low voltage can be reached. In such a case,
an external charger with discharge function may be used. Cadex Electronics
manufactures ’smart’ chargers and battery analyzers, both of which can be used
to test and calibrate the ’smart’ battery.

4. How to prolong&store batteries?

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 caused by
heat rather than charge/discharge patterns.
Although memory-free, apply a deliberate full discharge once every 30
charges to calibrate batteries with fuel gauge. Running down the battery in the
equipment does this. If ignored, the fuel gauge will become increasingly less
accurate. The battery life will not be affected.
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 date.Do not buy old stock, even if sold at clearance prices.

How to store batteries ?

Keep batteries in a cool and dry storage area. Refrigeration is recommended
but freezers should be avoided. When refrigerated, the battery should be placed
in a plastic bag to protect against condensation
Do not fully charge lithium and nickel-based batteries before storage. Keep
them partially charged and apply a full charge before use. Store lithium-ion at
about 40% state-of-charge (3.75-3.80V/cell open terminal). Lead-acid batteries
must be stored fully charged.
Do not store lithium-ion fully depleted. If empty, charge for about 30
minutes before storage. Self-discharge on a depleted battery may cause the
protection circuit to trip, preventing a recharge.
Do not stockpile lithium-ion batteries; avoid buying dated stock, even if
offered at a reduced price. Observe the manufacturing date, if available.
Never leave a nickel-based battery sitting on a charger for more than a few
days. Prolonged trickle charge causes crystalline formation (memory).

• Power down all nonessential functions. Switch it off if you’re not using it. Many business travelers already know that you don’t want to take the DVD player for a spin on the plane, and that every time you hit “save” it can set the hard-drive whirring, which devours even more power. “But users often also forget to turn off their wireless card when they are no longer using it but are still using their computer,” notes Mike Fuller, executive vice president of PC Laptops, a Sandy, Utah, laptop manufacturer. “When the wireless card is on, it still continually searches for networks.” In Windows XP, click on “Power Options” in your control panel. It allows you to reduce the power consumption of any number of your computer devices or of your entire system.
• Stay out of extreme temperatures. The technology that powers you battery isn’t terribly complicated. But it’s important to understand a little bit about the chemistry behind batteries, and how that can affect your work. Specifically, temperatures can affect the performance of your battery. It’s best to use (and especially charge) your batteries at room temperatures. Extreme conditions can drain your battery quickly. Also, avoid partial charges and use the battery until it is dead. Battery experts liken partial charges — and discharges — to eating a cup of lard every day. It significantly shortens your battery’s life. Considering that a lithium-ion battery can explode if it’s improperly used, it could also shorten your life.
• Let your laptop do the saving. Not every computing device handles a power source in the same way. Some of the more sophisticated laptops, which are designed with business travelers in mind, are misers when it comes to using power. And that’s a good thing — if you can remember to take advantage of it. “Most users make the mistake of simply not choosing to use a product’s built-in ability to conserve battery life,” says Dan Coffman, a senior product manager for PC manufacturer ViewSonic. How do you harness your PC’s built-in ability to save? Consult your user manual. Often, calibrating your laptop is as easy as double-clicking on the battery icon in the toolbar.
• Always, always carry a spare device that uses batteries. How obvious is that? Well, if you’re trying to keep under the onerous new airline weight-limits, it isn’t. But as Rick Thompson, director of engineering at Valence Technology in Austin, Texas, observes, “the availability of ‘free’ power outside of your hotel room is not predictable.” That’s a nice way of saying it. In fact, I sometimes think airport terminals, car-rental facilities and hotels try to hide the power outlets from us to keep us from accessing their free power. Thompson recommends a system that can simultaneously charge a second portable device such as a cell phone or PDA, allowing you to multitask your battery operations.