Laptop And PC Batteries

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). Click here for more info on battery run-time.

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. 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.

IMPORTANT NOTES:
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.

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.

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.

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.