How to service laptop batteries

How to service laptop batteriesregularly replaced. Such policy tends to satisfy the
Most laptops batteries are 'smart', meaning that somemanufacturer more than the user. Newer batteries
form of communications occurs between the batterygenerally do not have this feature.
and user. The definition of 'smart' varies amongIt is recommended to utilize the thermistor during
manufacturers and regulatory authorities. Somecharge and discharge to protect the battery against
manufacturers call their batteries 'smart' by simplyover heating. The thermistor can be measured with
adding a chip that sets the charger to the correctthe Ohmmeter. The most common thermistors are
charge algorithm. The Smart Battery System10 Kilo Ohm NTC or 10kOhm at 20°C (68°F). NTC
(SBS) forum states that a 'smart' batterystands for negative temperature coefficient, meaning
must provide state-of-charge (SoC) indications.that the resistance decreases with rising temperature.
A positive temperature coefficient (PTC) will increase
There are two common architectures of 'smart'the resistance. Warming the battery with your hand
batteries, consisting of the single wire system foundmay be sufficient to detect a small change in resistor
on high-end cameras and radio communicationsvalue.
devices, and the two-wire system typically used onAn SMBus battery contains permanent and
laptops. The two-wire system is usually configured totemporary data. The permanent data is programmed
the System Management Bus (SMBus). Because of itsinto the battery at time of manufacturing and
common use in laptops, we will focus on the SMBusincludes battery ID number, battery type, serial
system. Figure 1 shows the layout.number, manufacturer and date of manufacture. The
Figure 1: Two-wire SMBus system.temporary data is acquired during use and consists of
The SMBus is based on a two-wire system using acycle count, user pattern and maintenance
standardized communications protocol. This systemrequirements. Some of this information is renewed
lends itself to standardized state-of-charge andduring the life of the battery.
state-of-health measurements.Repairing a 'smart' battery
Battery connectionLaptop batteries can be repaired but the work is
The SMBus battery has five or more batteryoften time consuming. The success rate varies with
connections consisting of positive and negativebattery type. One must remember that the 'smart'
battery terminals, thermistor, clock and data. Thebattery consists of two parts, the chemical cells and
connections are commonly unmarked and attemptingthe digital circuit. In some cases, the chemical battery
to test this type of battery appears complicated.can be fully restored but the fuel gauge may be
Figure 2 describes the functions of a battery with 6inaccurate or its data is corrupt.
connections.
Figure 2: Connections of a typical laptop battery.Anyone attempting to repair SMBus battery must be
The positive and negative terminals are usually placedaware of some non-compliance. Unlike other tightly
on the outside; no norm exists on the arrangementregulated standards, the SMBus allows some
of the contacts.variations. This may cause problems with existing
The positive and negative battery terminals arechargers and the SMBus battery should be checked
commonly located at the outer edges of thefor compatibility before use. More information on
connector. The inner contacts accommodate theSMBus is available on and If the cells are weak, cell
clock and data. (On a one-wire system, clock andreplacement makes economic sense. While
date are combined.) For safety reasons, a separatenickel-based cells are readily available, lithium-ion cells
thermistor wire is brought to the outside. This allowsare not sold on the open market. This precaution is
temperature protection if the digital communication isunderstandable when considering the danger of
disabled.explosion and fire if the cells are assembled in a
Some batteries are equipped with a solid-state switchcareless way. Always replace the pack with the
that is normally in the off position. In such a case, nosame chemistry cells.
voltage is present. Connecting the switch terminal toDuring cell replacement, the circuit of the 'smart'
ground will turn the battery on. If this does not work,battery may need to be kept alive with a supply
a proprietary code may be needed to activate thevoltage. Disconnecting the circuit, if only for a fraction
battery. How can I find the correct terminals? Toof a second, can erase vital data and render the
begin with, use a voltmeter to locate the positivecircuit unusable. To assure continued operation when
and negative battery terminals. Establish the polarity.changing the cells, connect a secondary voltage
If no voltage is available, a solid-state switch maythrough a 100-Ohm resistor before disconnecting the
need to be activated. With the voltmeter connectedcells. Remove the secondary supply only after the
on the outer terminals, take a 100-Ohm resistorcircuit is fed from the new cells.
(other values may also work), connect one end ofThe open terminal voltages of the replacement cells
the resistor to ground, and with the other end touchshould be within 10% of each other. Welding the cells
each terminal while observing the voltmeter. If nois the only reliable way to get dependable service.
voltage appears, the battery may be dead or theAttention must be paid to limiting the amount of heat
pack requires a digital code to activate. The resistortransferred to the cells during welding. Excess heat
protects the battery against a possible electricalcan damage the cells.
short.During storage, each cell may have self-discharged to
Once the connection to the battery terminals isa different charge level. This is especially evident on
established, charging should be possible. If the chargenickel-based batteries. To assure proper charge of all
current stops after 30 seconds, an activation codecells without overcharging some, trickle charge the
may be required. This code is often difficult, if notnewly repaired pack for about 14 hours, then
impossible to obtain.discharge and recharge normally. Such a cycle is also
Some battery manufacturers even add anneeded to reset the battery's fuel gauge circuit.
end-of-battery-life switch. At a preset age, cycleLithium-ion can accept a normal charge in about 3
count or capacity level, the battery stops functioning.hours. The service should also include calibrating the
Manufacturers explain that customer satisfaction andbattery. (Refer to "Choosing the right battery for
safety can only be guaranteed if the battery isportable computing", Part Two).