8/2/2019 Understanding Battries

1/2

BATTERY The Offline Power

By Mukesh Joshi, Tech Point, Bhilwara (Raj) Mob: 92148-03404

BATTERY ABCs

There are thee main categories of computer batteries:

The first type of battery is the backup battery, which is commonly referred toas the "CMOS battery". This battery is what holds your computer's computersettings, such as the time and date. This allows your computer to rememberbasic computer settings and allows you to boot the computer without enteringthose settings each time you start the computer.

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

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

LI-ION BATTERIES

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

NICAD BATTERIES

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

LI-POLYMER

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

NIMH BATTERIES

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

SLA

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

8/2/2019 Understanding Battries

2/2

CHARGING INFORMATION

Most battery manufacturers recommend to slow charge a new NICAD batteryfor 24-hours before use. This initial trickle charge helps to redistribute theelectrolyte to remedy dry spots on the separator that may appear when theelectrolyte gravitates to the bottom of the cell during long storage. A slowcharge 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 differentcapacity levels during storage.

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

REFRESH INFORMATION

The recommended way to get the maximum performance from your laptopbattery. Refresh is the process of allowing your computer battery to draincompletely (to do this you will need to disable all power management utilities).

Once drained, recharge the battery to 100%. This will refresh all cells withinthe battery. Doing this every few months will help extend the life of yourportable computer battery.

DISCHARGE INFORMATION

The commonly used end-of-discharge voltage for the NICAD and NiMH is onevolt per cell. At that voltage level, most of the energy is spent and the voltagestarts to drop rapidly. Discharging a battery further could damage the battery

through cell reversal. Caution should be exercised when discharging a batterytoo deeply under heavy load.

The end-of-discharge voltage of the Li-ion needs to be carefully controlled andmust not, under any circumstances, go below 2.5V per cell. Protection circuitintrinsic to the Li-ion pack prevent the battery from being discharged belowthe safe limit. If allowed to self-discharge below 2.5V, unrecoverable capacityloss occurs when stored in that condition for three months or longer. Similar tothe 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 ina discharged state. The cells of a discharged SLA sulfate, a condition thatrenders the battery useless if left in that state for a few days.

Older batteries can by discharged by using a deep discharge