Battery Facts and FAQs

Laptop Batteries Facts & FAQs

Does using replacement batteries void the warranty of my device?

No! The Federal Trade Comission Magnoson-Moss Act states that a manufacturer cannot sell a product under the pretense that the consumer must purchase consumables, add-ons, replacement parts, etc. from the OEM in order to maintain their warranty. This pratice is called "Tie-In Sales" and is strictly prohibited.

Therefore, by law, manufacturers cannot threaten to void your warranty or use scare tactics to prevent you from purchasing batteries from

How is a lithium battery different from an alkaline battery?

The difference between alkaline and lithium batteries is that the battery chemistry and construction differ in the two systems. Since lithium is a very active material, it provides a great deal of power relative to the amount of material used in a battery. The lithium discharge curve is longer and flatter than alkaline, providing a consistently higher voltage throughout the life of the battery.

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What is the difference between Lithium batteries and Lithium Ion batteries?

There are several important differences. The practical difference between Lithium batteries and Lithium-ion (Li-ion) batteries is that most Lithium batteries are not rechargeable but Li-ion batteries are rechargeable. From a chemical standpoint Lithium batteries use lithium in it's pure metallic form. Li-ion batteries use lithium compounds which are much more stable than the elemental lithium used in lithium batteries. A lithium battery should never be recharged while lithium-ion batteries are designed to be recharged hundreds of times.

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What are the advantages of Lithium Ion batteries compared to other rechargeable batteries?

Lithium-ion batteries have several advantages: They have a higher energy density than most other types of rechargeables. This means that for their size or weight they can store more energy than other rechargeable batteries. They also operate at higher voltages than other rechargeables, typically about 3.7 volts for lithium-ion vs. 1.2 volts for NiMH or NiCd. This means a single cell can often be used rather than multiple NiMH or NiCd cells. Lithium-ion batteries also have a lower self discharge rate than other types of rechargeable batteries. This means that once they are charged they will retain their charge for a longer time than other types of rechargeable batteries. NiMH and NiCd batteries can lose anywhere from 1-5% of their charge per day, (depending on the storage temperature) even if they are not installed in a device. Lithium-ion batteries will retain most of their charge even after months of storage. So in summary; lithium-ion batteries can be smaller or lighter, have a higher voltage and hold a charge much longer than other types of batteries.

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What is the difference between Nickel Cadmium (NiCad) and Nickel Metal Hydride (NIMH) batteries? What is "Memory Effect?"

Both NiCad and NiMH batteries are rechargeable. The main difference between the two is the fact that NIMH batteries offer higher energy densities than NiCads. In other words, pound for pound, NIMH delivers approximately 30% more capacity than its NiCad counterpart. What this translates into is increased runtime from the battery with no additional bulk. NIMH also offers another major advantage: NiCad batteries tend to suffer from what is called a "memory effect". What this means is that when a NiCad battery is only partially discharged before charging, the battery "forgets" that it has the capacity to further discharge all the way down.

To illustrate: If you, on a regular basis, fully charge your battery and then use only 40% of its capacity before the next recharge, eventually the battery will become unaware of its extra 60% capacity which had remained unused. Your battery will remain functional, but only at 40% of its original capacity.

The way to avoid the dreaded "memory effect" is to fully cycle your NiCad battery at least once a month. In other words, fully discharge your battery and then fully charge it.

Batteries can be discharged by allowing the device to run on the battery until it ceases to function. This will insure your battery remains healthy. NIMH batteries are "memory free" - they do not suffer from this affliction. Thus, if you have a NIMH battery, the only time it is necessary to cycle it is during its initial use and after a long storage period. This is done to "exercise" the battery and bring it up to full capacity.

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I just received my battery from and it isn't fully charged.

New batteries are shipped in a discharged condition and must BE charged before use. We generally recommend an overnight charge (approximately twelve hours) for NiCad batteries and a 24 hour charge for Nickel Metal Hydride. Refer to your manual for charging instructions. Rechargeable batteries should be cycled - fully charged and then fully discharged - 2 to 4 times initially to allow them to reach their full capacity. (Note: it is perfectly normal for a battery to become warm to the touch during charging and discharging).

Rechargeable lithium batteries, such as Lithium Ion (Li-Ion) and Lithium Polymer (Li-Poly) are also shipped in a discharged condition. ICAO/IATA regulations will limit the state of charge to 30% for shipping, so you will need to fully charge these batteries once you receive them to maintain them.

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How long should my new rechargeable battery last?

The life of a battery operating under normal conditions should be between 500 to 800 charge-discharge cycles. This translates into one and a half to three years of battery life for the average user. As your rechargeable battery begins to die, you will notice a decline in the running time of the battery. When your two hour battery is only supplying you with twenty minutes worth of use, it is time for a new one. NiCad and NIMH batteries have an average shelf life of three to four years. When a battery is not used for extensive periods of time it should be removed from the computer and stored in a cool, dry and clean environment. Self-discharge will occur when the battery is not used for an extended time period. Fully charge the battery before use after storage.

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How to safely jump start a battery with booster cables:

  • Always wear proper eye protection.
  • Never lean over battery.
  • Do not jump start a damaged battery
  • Inspect both batteries before connecting booster cables.
  • Be sure vent caps are tight and level.
  • Place a damp cloth over the vent caps of both car batteries.
  • Make certain that the vehicles are not touching and both ignition switches are turned to the "OFF" position:

  • Jump Starting a Battery

  1. Connect positive (+) booster cable to positive (+) terminal of discharged battery.
  2. Connect other end of positive (+) cable to positive (+) terminal of assisting battery.
  3. Connect negative (-) cable to negative (-) terminal of assisting battery.
  5. Start vehicle and remove cables in REVERSE order of connections.

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Does it really help to store batteries in the refrigerator?

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, C, AA, AAA, 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.

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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.

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How do I recycle my battery?

NiCD and NiMH batteries should be recycled properly. Do NOT throw these batteries in the trash. NiCD 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.

Battery Mart accepts the following types of Consumer Batteries for Recycling-Shipped Prepaid to our location:

Please contact us for quantities over 12 batteries


*We can provide contact information for companies that accept these.

Please call us at 800-405-2121 or email us at [email protected] for more information and return procedures.

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Traveling by air with your battery

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.

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Three simple maintenance tips assure longer life For wet lead acid batteries:

  1. 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.
  2. 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.
  3. Recharge your battery as soon as possible after discharge; never leave it discharged for an extended period of time.

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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.

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What are main batteries?

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).

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What are CMOS or clock batteries?

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 (NiCad) 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 NiCad 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.

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What are RAM or resume batteries?

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 NiCad or NiMH and will last around 2-3 years. It is recommended that you replace your notebook's RAM battery when replacing the CMOS battery.

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How long will the new main battery power the laptop?

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.

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Is it possible to upgrade the device's battery to a newer chemistry?

NiCad, NiMH 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.

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What is a "Smart" battery?

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.

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Maximizing your battery's performance

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. NiCad, NiMH 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.

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NiCad 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 NiCad will result in a nonfunctional battery because the computer lacks the proper charging circuitry to charge the NiCad battery.

If a motherboard lacks the above-discussed male pins for an external battery, the NiCad battery MUST be unsoldered and replaced by a NiCad battery ONLY. Attempting to use an alkaline or lithium battery in place of NiCad 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.