Frequently Asked Questions:

1. Basic knowledge about battery.

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).