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Laptop Battery Facts & F.A.Qs

Important Information

Q: What are Main Batteries?

A: The main battery (also called the power battery) is the battery pack which allows a laptop or notebook to operate independently of an AC power source. These rechargeable batteries are designed to operate the computer for a certain amount of time (generally 1 to 4 hours).

Q: What are CMOS or Clock Batteries?

A: CMOS & Clock Backup batteries perform the same function in desktop and laptop computers: when the computer is turned off, the battery maintains the time and date, thus insuring their accuracy when the system is once again restarted. More importantly, the battery saves the computers BIOS setup configuration, which allows the system to efficiently reboot once it is restarted. The computer knows what type of hard drive it is dealing with, etc. Not surprisingly, these batteries are known alternatively as CMOS batteries, Real Time Clock (RTC) batteries, or simply internal batteries.

The most common CMOS battery chemistries are Lithium, Nickel Cadmium (Ni-Cd) and alkaline. They are usually somewhere in the 3 to 7.2 volt range and either solder onto the motherboard or plug in via a snap-in connector (depending upon the computer manufacturers design).

In most cases, replacement of the CMOS battery is an easy task. It is simply a matter of locating the battery on the computer's motherboard, removing it and plugging in a new one. As a rule, internal batteries should be replaced by the same type of battery which was originally used in the machine or according to the manufacturers specifications. The major exception to this rule are older PCs which were manufactured with a Ni-Cd battery soldered onto the motherboard. These computers usually have a three or four pin male plug, with two of the pins connected via a jumper (this is generally found in the same area of the motherboard as the original battery). This plug gives you the option of leaving the soldered battery in place and replacing it with a plug-in lithium or alkaline battery. Removing the jumper tells the computer to ignore the soldered battery and to look to the pins for its power source. If the motherboard has this provision, you can install a standard PC plug-in battery instead of removing the soldered battery and re-soldering a new one (the standard PC plug-in battery is Electro Battery part number BAT 2005 (lithium) or BAT B40 (alkaline). These batteries are interchangeable).

A word of warning:
some computers have 4 pins on the motherboard, whereas today's plug-in batteries come with a 3 pin connector (one of the pinholes is closed in order to prevent the user from inadvertently plugging the battery in with reversed polarity). If this is the case, you should clip the pin from the motherboard that corresponds to the sealed pinhole on the battery plug. That pin is nonfunctional and by clipping it you ensure that future batteries will not be installed on the motherboard with reversed polarity.


Ni-Cd batteries are rechargeable, whereas Lithium and alkaline batteries are NOT. Therefore, Lithium and alkaline batteries must be replaced by equivalent batteries of the same type. Attempting to replace these non-rechargeable batteries with a Ni-Cd will result in a nonfunctional battery because the computer lacks the proper charging circuitry to charge the Ni-Cd battery.

If a motherboard lacks the above-discussed male pins for an external battery, the Ni-Cd battery MUST be unsoldered and replaced by a Ni-Cd battery ONLY. Attempting to use an alkaline or lithium battery in place of Ni-Cd on such a board could be hazardous. These batteries are not designed to be recharged, and an attempt to do so may cause the battery to "burst", or explode.

CMOS batteries generally last for two to three years, although some (especially the lithium type) have been known to last much longer. Ironically, the less the computer is used the faster the CMOS battery will run out. This is because when the computer is turned off the battery begins to function. It is recommended to replace the CMOS battery approximately once every two years or when servicing the computer. If the computer has been idle for an extended length of time it is a good idea to change the battery. Changing the battery is a relatively easy and inexpensive task, especially (as were sure many of you out there know) when compared to trying to reboot and configure a computer which has lost its BIOS settings.

Q: What are RAM or Resume batteries?

A: Some notebook computers are designed with a dedicated battery for backing up RAM (random access memory) functions when the machine temporarily loses power from the main battery. This feature allows users to change the main battery pack without losing the current applications and settings residing in memory. This is called a "battery hot swap" - switching the main battery pack without having to turn off the computer.

These type of batteries are alternately known as bridge batteries, RAM batteries, auxiliary batteries or resume batteries.

Most RAM batteries are rechargeable Ni-Cd or Ni-MH and will last around 2-3 years. It is recommended that you replace your notebook's RAM battery when replacing the CMOS battery.

Q: How Long Will the New Main Battery Power the Laptop?

A: Battery run-time on a laptop is difficult to determine. Actual battery running time depends upon the power demands made by the equipment. The use of the screen, the hard drive and other accessories results in an additional drain upon the battery, effectively reducing its running time. The total run-time of the battery is also dependent upon the design of the equipment. Generally, a new Hi-Capacity battery will run 30% to 50% longer than the old battery did when it was new.

Q: Is it Possible to Upgrade the Device's Battery to a Newer Chemistry?

A: Ni-Cd, Ni-MH and Li-ion are all fundamentally different technologies and cannot be substituted for one another unless the device has been pre-configured from the factory to accept more than one type of rechargeable battery. The difference between them stems from the fact that each technology requires a different charging pattern to be properly recharged. Therefore, the portable device's charger must be properly configured to handle a given type of rechargeable battery.

Refer to the owners manual to find out which rechargeable battery types the particular device supports or use our QuickFind search engine to find the device in our database. The database will automatically list all of the battery types supported by the machine.

Q: What is a "smart" Battery?

A: Smart batteries have internal circuit boards with smart chips which allow them to communicate with the notebook and monitor battery performance, output voltage and temperature. Smart batteries will generally run 15% longer due to their increased efficiency and also give the computer much more accurate "fuel gauge" capabilities to determine how much battery running time is left before the next recharge is required.

Q: How Can I Maximize Battery Performance?

A: There are several steps you can take to insure that you get maximum performance from the battery:
  • Break In New Batteries
    New batteries come in a discharged condition and must be fully charged before use. It is recommended that you fully charge and discharge the new battery two to four times to allow it to reach its maximum rated capacity.
  • Prevent the Memory Effect
    Keep the battery healthy by fully charging and then fully discharging it at least once every two to three weeks. Exceptions to the rule are Li-ion batteries which do not suffer from the memory effect.
  • Keep the Batteries Clean
    It's a good idea to clean dirty battery contacts with a cotton swab and alcohol. This helps maintain a good connection between the battery and the portable device.
  • Exercise the Battery
    Do not leave the battery dormant for long periods of time. We recommend using the battery at least once every two to three weeks. If a battery has not been used for a long period of time, perform the new battery break in procedure described above.
  • Battery Storage
    If you don't plan on using the battery for a month or more, we recommend storing it in a clean, dry, cool place away from heat and metal objects. Ni-Cd, Ni-MH and Li-ion batteries will self-discharge during storage; remember to break them in before use. Sealed Lead Acid (SLA) batteries must be kept at full charge during storage. This is usually achieved by using special trickle chargers. If you do not have a trickle charger, do not attempt to store SLA batteries for more than three months.
  • For Notebook Users
    To get maximum performance from the battery, fully optimize the notebooks power management features prior to use. Power management is a trade off: better power conservation in exchange for lesser computer performance. The power management system conserves battery power by setting the processor to run at a slower speed, dimming the screen, spinning down the hard drive when it's not in use and causing the machine to go into sleep mode when inactive. The notebook users guide will provide information relating to specific power management features.

Storing Your Battery for Long Periods of Time:

If you use your battery for seasonal activities only and must store it for extended periods of time, a battery maintainer is recommended. A maintainer is an electronically controlled charger and will not over charge your battery when hooked up for extended periods of time. Your battery will be ready for use when you are and last longer.

Maintainers are also great for winter starting - A fully charged battery has maximum

Starting Power!
  1. Charge the battery until it is completely charged.
  2. Store it in as cold as possible but not where it will consistently go below 32 F. All batteries lose some charge when stored, but the lower the temperature, the lower the self discharge.
  3. Check the battery every two months and recharge if necessary.


Q: How do I Dispose of my battery?

A: Nicad and NIMH batteries should be disposed of property. Do NOT throw these batteries in the trash. Ni-Cd batteries are composed of approximately 20% cadmium, an extremely hazardous element which is environmentally detrimental. While NIMH batteries are environmentally friendly, the higher capacity NIMH cells still contain trace amounts of cadmium. Be environmentally conscious. Recycle your batteries.


Do NOT short-circuit or disassemble your battery. A short-circuit may cause severe damage to the battery. Do not drop, hit or otherwise abuse the battery. This behavior may result in the exposure of the cell contents, which are corrosive. Do not expose the battery to moisture or rain. Keep battery away from fire or from other sources of extreme heat. Do not incinerate. Exposure of battery to extreme heat may result in an explosion.


Certain batteries (i.e. lithium or wet-filled with acid-electric storage), when transported via air have to be properly declared to the air carrier, marked, labeled, and packaged per the Hazardous Materials Regulations. At a minimum, all battery types must be packaged securely and in a manner that prevents the dangerous evolution of heat, for example, by effective insulation of exposed terminals.

Three Simple Maintenance Tips Assure Longer Life For Wet Lead Acid Batteries:

Regularly clean the battery top and terminals. Apply baking soda to any corrosion and flush entire cover with water. Be sure the vent caps are tight before cleaning to prevent water or baking soda from entering into the cells.
  1. Check your battery's water level before charging and if the level is low, add sufficient (distilled) water to cover the plates. After charging, check and add distilled water to bring level up to the bottom of the vent walls. DO NOT OVERFILL. Distilled water is best for long battery life...but if not available, use a good grade of drinking water.
  2. Recharge your battery as soon as possible after discharge; never leave it discharged for an extended period of time.

Q: Does it really help to store batteries in the refrigerator?

A: Yes, but only if they can be kept dry as well. The higher the temperature, the more the free flow of ions or self-discharge from the battery. Storing primary batteries (D's, C's, AA's, AAA's, 9 volt, etc.) in a cooler environment slows down this rate of discharge that all batteries experience even when not in use, hence a longer shelf life. However, if this is done, it is important that the batteries be kept as dry as possible by keeping them in an airtight container in the driest part of the refrigerator, the door for example. Long term exposure to moisture inside the refrigerator can cause internal corrosion to the battery. When removing batteries from the refrigerator, allow them to warm up to room temperature before using them in your device.
How can batteries be connected?
Note: When interconnecting batteries (cells), they must be identical in voltage and amp rating!
Batteries may be connected in series. The positive terminal of the first battery is connected to the negative terminal of the second battery; the positive terminal of the second is connected to the negative of the third, and so on. The voltage of the assembled battery is the sum of the individual batteries. The batteries are connected: + to - to + to - to + to -, etc. The capacity of the battery is unchanged.
Batteries may also be connected in parallel. The positive terminal of the first battery is connected to the positive terminal of the second battery, the positive terminal of the second is connected to the positive of the third; the negative terminal of the first battery is connected to the negative terminal of the second battery, the negative terminal of the second is connected to the negative of the third and so on. The batteries are connected: + to + to + and - to - to -. In this configuration, the capacity is the sum of the individual batteries and voltage is unchanged.
For example, (5) 6V 10AH batteries connected in series produces a battery array that is 30 Volts and 10AH. Connecting the batteries in parallel produces a battery array that is 6 Volts and 50AH. Ordinary auto batteries are designed in the same fashion. Six 2-volt cells are arranged in series to produce a 12v battery. Many Ni-Cd batteries are arranged in the same way.
The rating for battery
V(olts):The voltage of the new battery should always match the voltage of the original.
mAh:It standards for milli-Amp hours(1 mAh=0.001Ah),Hight amp-hour ratings means a longer run-time and will not cause incompatibilities.
How do I charge my batteries?
Our Ni-MH chargers are fully automatic. Plug your charger into an A/C (or D/C power source for the Powerex MH-C204F-DC) and place your batteries into the charger in matched pairs of two or four batteries to begin charging. Red lights indicate charging in progress. The lights will turn green when charging is complete and the charger will automatically switch to a trickle charge. The trickle charge will keep your batteries fully charged and ready for use. Refer to our Charger Manuals page for more detailed operating instructions for your model charger.
What is a battery cycle?
Cycle life is measured by the amount of times a battery may be charged and discharged. Every time a battery is charged and discharged, it uses one cycle. Cycle life is very important in battery applications such as laptop batteries and emergency light batteries. A Ni-Cd battery has a cycle life of 500-1000 or more cycles.
Can I use my older Ni-Cd battery charger to charge my Ni-MH batteries?
No, you can use a newer Ni-MH charger to charge your old Ni-Cd batteries but you should not try to charge Ni-MH batteries with a Ni-Cd charger. Here's why: Ni-MH and Ni-Cd batteries are chemically very similar and when both are fully charged the battery voltage will start to drop. The Ni-MH voltage drop is much more subtle and more difficult to detect. Ni-MH chargers usually have an overtemperature sensor and shutoff to prevent overcharge as well as a more sensitive voltage drop detector where Ni-Cd chargers usually only use the voltage drop to determine when to stop charging. If you charge Ni-MH batteries in a Ni-Cd charger it will probably miss the voltage drop and keep right on charging causing the batteries to overheat. Overcharge and overheating Ni-MH batteries can damage them internally and reduce battery life.

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