Basic Questions about Battery

A battery is a device that generates an electrical current by electrochemical reaction.

A battery pack is an assortment of two or more battery cells, configured in a predefined order - a series, parallel or a mixture of both - to deliver the desired voltage, capacity, or power density.

Volt (V), short for voltage, is a measure of electrical force or electrical pressure. The terminal voltage, measured in volts, of a battery is the electrical potential difference across its two terminals. Battery cells of different chemistries have different voltages. A nickel-based cell, like NiCd and NiMH, provides a nominal cell voltage of approximately 1.2 V and a Li-ion cell provides 3.6V/3.7V.

The voltage of two battery cells, of the same chemistry, is always the same. Their capacities may be different, but the voltage always remains the same. Higher terminal voltages are obtained by assembling two or more cells in a series, parallel or a mixture of both. For example, a 7.4V, Li-ion battery would be made up of 2 cells connected in a series. 2 cells x 3.7V Li-ion cell = 7.4V Li-ion battery

It is important that the voltage of a cell or a battery pack always matches the voltage requirement of the device in which it is used. If there is any mismatch of the two voltages, the device will not function. Excessive exposure to a different voltage may also damage the equipment. Equipment users should take special care that the batteries they are using matches the voltage requirement of their device.

The capacity of a battery is its electrical energy content usually expressed in milliAmpere-Hours (mAH). It is determined by the amount of electrical energy the battery can deliver, under specified conditions of temperature, rate of discharge and final battery voltage, over a certain period of time.

Higher the capacity rating of a battery, i.e. higher the mAH, longer the battery will last. For example, a battery rated at 1000mAH capacity will last for 1 hour in a device that draws current of 1000mAH and a battery rated at 2000mAH capacity will last for 2 hours in the same device.

For portable devices like laptops that are used for long periods of time, a high capacity battery provides a clear advantage. A high capacity battery would give a longer runtime and reduce downtimes due to unexpected battery failures.

Ampere (Amp) is a measure of electrical current flow. It is the rate of flow of electricity through a specific point in one second.

It is a unit of measurement of battery capacity, i.e. the amount of power packed into a battery. It is obtained by multiplying the current in miliamperes (mA) by the length of time that the current is flowing, abbreviated mAH. Higher "mAH" rating means higher battery capacity, which results in longer battery life between charges.

No! Lithium ion batteries are not affected by "Memory effect", which results in a drop in the capacity or voltage of a rechargeable battery. Memory effect is confined only to nickel-based battery chemistries like NiCd and NiMH. For users of portable devices like laptops, unexpected downtimes due to battery failures could be very frustrating.

Battery cycle life is the number of times a battery can be charged and discharged before it fails to meet specified criteria as to performance. One battery cycle is defined as a full charge followed by a full discharge.

Self-discharge is the loss of charge in a battery when not in use. Unused batteries lose their charge over time. The loss of charge, or self-discharge, is the highest right after charge when the battery holds full capacity. Other factors like humidity and temperature of the storage place also contributes to the rate of self-discharge.

All battery chemistries self-discharge. Li-ion batteries have the lowest self-discharge rate at 5% to 10% per month as compared to NiCd, at 20% per month, and NiMH, at 30% per month, under identical conditions.

Clean contacts: To achieve optimum charge contact, be sure both charger and battery contacts are clean. Dirty contacts can result in a charger/battery malfunction.

Optimum charging temperature: Lithium-ion batteries should be charged in room temperatures between 0^oC and 45^oC for optimum battery performance.

Charging voltage: Li-ion batteries have an inbuilt protection circuit that automatically cuts off the current path if the battery voltage reaches above 4.2 volts/cell. Equipment users should avoid charging their Li-ion batteries to this limit to improve cycle life.

Laptop batteries should be removed from their equipment and stored separately in a clean, dry and cool place away from heat and metal objects. The batteries should be discharged to 40% charge level for storage. As batteries self-discharge when not in use, prolonged storage of Li-ion batteries for more than three months is not recommendable.

It is the number of battery cycles, a full charge followed by a full discharge, a battery can offer before it needs to be replaced. Li-Ion batteries generally offer around 300 charge/discharge cycles.