Information on computer batteries

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Battery ABCs
Li-ion batteries
NICAD batteries
Li-polymer batteries
NiMH batteries
SLA batteries
Battery chemistry
Charging information
Refresh information
Discharge information
Battery Recycling
Battery definitions
Technical Support

BATTERY ABCs

There are thee main categories of computer batteries:

The first type of battery is the backup battery, which is commonly referred to as the "CMOS battery". This battery is what holds your computer's computer settings, such as the time and date. This allows your computer to remember basic computer settings and allows you to boot the computer without entering those settings each time you start the computer. Additional information about CMOS and the CMOS batteries can be found on our CMOS help page.

The second type of battery is the "bridge battery". This battery is only found within portable computers and is used as a temporary backup for the main battery. This allows you to remove the main battery and replace it with a good battery without having to turn off the computer.

The third type of battery is the main battery. The main battery is also only used with portable computers and is used as an alternate source of power for when the computer is not connected to a standard wall outlet.

LI-ION BATTERIES

(Lithium Ion) fragile technology requiring protector circuit, the Li-ion is used where very high energy density is needed and cost is secondary.

NICAD BATTERIES

(Nickel Cadmium) is a well known and understood battery. The NICAD is used where long life, high discharge rate and economical price are important.

LI-POLYMER

(Lithium Polymer) a potentially lower cost version of the Li-ion under development and has not yet been released to the public.

NIMH BATTERIES

(Nickel -Metal Hydride) provides incremental improvements in capacity over the NICAD at the expense of reduced cycle life and lower load current.

SLA

(Sealed Lead Acid) most economical for larger power applications where weight is of lesser concern.

Most battery manufacturers recommend to slow charge a new NICAD battery for 24-hours before use. This initial trickle charge helps to redistribute the electrolyte to remedy dry spots on the separator that may appear when the electrolyte gravitates to the bottom of the cell during long storage. A slow charge also helps to bring all the individual cells within a battery pack up to an equal charge level because each cell may have self-discharged to different capacity levels during storage.

Note: Today's newer NICAD batteries may not this initial charge. Refer to the products documentation for proper charging steps. 

REFRESH INFORMATION

The  recommended way to get the maximum performance from your laptop battery. Refresh is the process of allowing your computer battery to drain completely (to do this you will need to disable all power management utilities). Once drained, recharge the battery to 100%. This will refresh all cells within the battery. Doing this every few months will help extend the life of your portable computer battery.

Some laptop manufactures also include a battery refresh through the CMOS setup. See document CH000192 for information about entering the CMOS setup.

DISCHARGE INFORMATION

The commonly used end-of-discharge voltage for the NICAD and NiMH is one volt per cell. At that voltage level, most of the energy is spent and the voltage starts to drop rapidly. Discharging a battery further could damage the battery through cell reversal. Caution should be exercised when discharging a battery too deeply under heavy load.

The end-of-discharge voltage of the Li-ion needs to be carefully controlled and must not, under any circumstances, go below 2.5V per cell. Protection circuit intrinsic to the Li-ion pack prevent the battery from being discharged below the safe limit. If allowed to self-discharge below 2.5V, unrecoverable capacity loss occurs when stored in that condition for three months or longer. Similar to the NiMH and SLA, more cycles can be obtained by partially, rather than fully, discharging the Li-ion battery.

The SLA should not be discharged beyond 1.75V per cell, nor can it be stored in a discharged state. The cells of a discharged SLA sulfate, a condition that renders the battery useless if left in that state for a few days.

Older batteries can by discharged by using a deep discharge debug routine found at our Debug page.

1997