How to Repair a Laptop Battery

Most laptop batteries are smart. This means that the pack consists of two parts: the chemical cells and the digital circuit. If the cells are weak, cell replacement makes economic sense. While nickel-based cells are readily available, lithium-ion cells are commonly not sold over the counter, and most manufacturers only offer them to authorized pack assemblers. This precaution is understandable given liability issues. Read also about Safety Concerns and Protection Circuits. Always use the same chemistry; the mAh rating can vary if all cells are replaced.

A laptop battery may have only one weak cell, and the success rate of replacing the affected cell depends on the matching with the others. All cells in a pack must have a similar capacity because an imbalance shortens the life of the pack. Read more about Can Batteries Be Restored?. Furthermore, the state-of-charge of all cells being charged for the first time should have a similar charge level, and the open-circuit voltages should be within 10 percent of each other. Welding the cells is the only reliable way to get dependable connection. Limit the heat transfer to the cells during welding to prevent excess heat buildup.

The typical SMBus battery has five or more battery connections consisting of positive and negative battery terminals, thermistor, clock and data. The connections are often unmarked; however, the positive and negative are commonly located at the outer edges of the connector and the inner contacts accommodate the clock and data. (The one-wire system combines clock and data.) For safety reasons, a separate thermistor wire is brought to the outside. Figure 1 illustrates a battery with six connections.

Terminal connection of a typical laptop battery

Figure 1: Terminal connection of a typical laptop battery

The positive and negative terminals are usually placed on the outside; no norm exists on the arrangement of the other contacts.

Courtesy of Cadex

Some batteries are equipped with a solid-state switch that is normally in the “off” position and no voltage is present on the battery terminals; connecting the switch terminal to ground often turns the battery on. If this does not work, the pack may need a proprietary code for activation, and battery manufacturers keep these codes a well-guarded secret.

How can you find the correct terminals? Use a voltmeter to locate the positive and negative battery terminals and establish the polarity. If no voltage is available, a solid-state switch in the “off” position may need activating. Connecting the voltmeter to the outer terminals, take a 100-Ohm resistor (other values may also work), tie one end to ground, and with the other end touch each terminal while observing the voltmeter. If no voltage appears, the battery may be dead or the pack will require a security code. The 100-Ohm resistor is low enough to engage a digital circuit and high enough to protect the battery against a possible electrical short.

Establishing the connection to the battery terminals should now enable charging. If the charge current stops after 30 seconds, an activation code may be required, and this is often difficult if not impossible to obtain.

Some battery manufacturers add an end-of-battery-life switch that turns the battery off when reaching a certain age or cycle count. Manufacturers argue that customer satisfaction and safety can only be guaranteed by regularly replacing the battery. Such a policy tends to satisfy the manufacturer more than the user, and newer batteries do not include this feature.

If at all possible, connect the thermistor during charging and discharging to protect the battery against possible overheating. Use an ohmmeter to locate the internal thermistor. The most common thermistors are 10 Kilo Ohm NTC, which reads 10kΩ at 20°C (68°F). NTC stands for negative temperature coefficient, meaning that the resistance decreases with rising temperature. In comparison, a positive temperature coefficient (PTC) causes the resistance to increase. Warming the battery with your hand may be sufficient to detect a small change in resistor value when looking for the correct terminal on the battery.

In some cases the chemical battery can be restored, but the fuel gauge might not work, is inaccurate, or will provide wrong information. After repackaging, the battery may need some sort of initialization/ calibration process. Simply charging and discharging the pack to reset the flags might do the trick. A “flag” is a measuring point to mark and record an event.

 The circuits of some smart batteries must be kept alive during cell replacement. Disconnecting the voltage for only a fraction of a second can erase vital data in the memory. The lost data could contain the resistor value of the digitized shunt that is responsible for the coulomb counter. Some integrated circuits (IC) responsible for fuel gauge function have wires going to each cell, and the sequence of assembly must to be done in the correct order.

To assure continued operation when changing the cells, supply a secondary voltage through a 100-Ohm resistor to the circuit before disconnection and remove the supply only after the circuit receives voltage again from the new cells. Cell replacement of a smart battery has a parallel with open-heart surgery, where doctors must keep all organs of the patient alive.

Anyone repairing an SMBus battery needs to be aware of compliance issues. Unlike other tightly regulated standards, the SMBus allows some variations, and this can cause problems when matching battery packs with existing chargers. The repaired SMBus battery should be checked for compatibility before use. More information on SMBus is available on www.sbs-forum.org and www.acpi.info.

Simple Guidelines when Repairing Battery Packs

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Comments

On March 7, 2011 at 7:00am
mahmood jaser wrote:

hello
i have a laptop battery(10.8volts ,55Wh ) with samsung cells ICR18650-26A
and another laptop battery(10.8 volts ,47Wh,4200mAh)with Sony cells is it posiible to replace each one with the other ? is there will be any damage to my laptop ? what is the meaning of (Wh and mAh )and what is the difference between the two baterries and cells discribed above?
please answer me

On March 11, 2011 at 9:19pm
samir wrote:

no its never ever possible

On April 19, 2011 at 12:38am
Ramya wrote:

1.Can the laptop be used without battery but being plugged in?
2.If battery is charged fully but stilled being plugged in, what is the risk?
3.In certain circumstances of updating, Windows needs th laptop to be plugged in,why is it necessary/

On April 22, 2011 at 5:22pm
Nuno wrote:

Ramya,
answers:
1 -Can the laptop be used without battery but being plugged in?
yes it can. Of course in the event of power failure it will go off on the moment.

2.If battery is charged fully but stilled being plugged in, what is the risk?
  Almost none. Li-ion batteries permanently lose capacity. The rate of losing capacity is proporcional to temperature. IF they are exposed to hot temperatures they will have shorter lifes. So, best way to prolong battery life is to charge it to full capacity and store it in the fridge when not needed. Its not very practical dough.

3.In certain circumstances of updating, Windows needs th laptop to be plugged in,why is it necessary/
This happens whenever the time expected to complete the operation is very long. So, if the computer was being run on battery it would be probable it will discharge before the task was done.

On May 25, 2011 at 10:39pm
mario henry corea v wrote:

estudiare esto detenidamente para evitar errores personales gracias por enseñarme

On June 1, 2011 at 5:26am
Arthur Anthony wrote:

Please how can i get the chemical cells for laptop battery

On June 18, 2011 at 10:09am
jayville wrote:

Pls Help me with dis….. (1) i;ll like to charge my fone with a dell laptop battery whenever theres no power. can i connect my charger bit to the positive and negative direct to the battery? (2) how to i recharge the laptop battery itself. Can i do this with the charge system in an rechargeable torch?

On June 22, 2011 at 5:30am
Leo Cai wrote:

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Toshiba PA3399…......$17.81     10.8V   4400mAh
Sony BPS8…............$26.5     11.1V     4400mAh
Apple A1175:............$23.32       11.1V   5800mAh

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On July 11, 2011 at 5:30pm
Steve wrote:

Hello,

I was inquiring about the C7000 series in order to wake up a couple Dell laptop batteries that have resisted taking any charge after being away from the laptop for an extended period of time.

I was given the following as part of the response:

“Testing Dell Laptop batteries, can however, be a challenge as in many cases they have a protection circuit in the batteries which doesn’t allow it to “handshake” or communicate with the analyzer to get the charge going.”

1. Is there any reliable way to get around the handshake issue?

2. How do I know which Dell laptop batteries have that problem?

3. I understand it was only the older laptop batteries and not the newer
ones that are affected. Is that correct?

Thanks,

Steve

On September 7, 2011 at 8:28am
Ramya wrote:

Though Battery is fully charged…
System shut downs after 15-20 minutes…
But If plugged in works properly..
What would be the problem?

On September 20, 2011 at 7:22am
warren huntley wrote:

sasnyo makes a barret [eneloop] that holds a charg to 85% over a yr. why cant this type batt. be used in comp. with lithium batt. they have ashort shelf life because of internal loss do to impureities in manufacture ,sonyo uses nano technoligy ,

On September 24, 2011 at 8:25am
Doug wrote:

I have a PowerBook g4. The power port on My dc in power board where my power cord plugs in has gone bad. Apple doesn’t make the part anymore so now I’m stuck with a computer that can’t power up. I saw that they sell an external battery charger for all laptops. Is it possible to use my existing power cord and hook it up to my battery to charge it? If yes can you describe in detail how to do so?

On January 7, 2012 at 3:24pm
SPG wrote:

Hi.
is there any way of connecting charger instead of battery?
my laptop doesn’t work from charger but works on battery - can i remove battery and connect charger there to laptop instead of battery?

On January 7, 2012 at 7:20pm
Munna wrote:

One of hcl laptop battery which battery backup time is very much less than expected. No how i improve my btry life.

model is c4500BAT-6 (LI-ION btery pack) is
pls answer me.

On January 20, 2012 at 6:39pm
Munna wrote:

Pls ans. Me.

On February 19, 2012 at 3:20pm
shkenca wrote:

Hi,

I found this site very helpful,
however I still I am not sure hoe to remove the old cells without disconnecting the chip from power. Anyone help me to find wires that feed the chip.
thanks, looking forward for help on this issue

On February 19, 2012 at 3:29pm
shkenca wrote:

Any advice or idea where to get extra tabs, while I build the new battery, besides those that are attached to the cells and others that i sav from the old battery.

thanks

On February 19, 2012 at 3:31pm
shkenca wrote:

Hi,
Any advice or idea where to get extra tabs, while I build the new battery, besides those that are attached to the cells and others that i sav from the old battery.

thanks

On March 1, 2012 at 4:55am
Yason wrote:

I have Dell latitude 620d

From 3 days ago, my Laptop can’t connect the battery..
First i see 100 %..
But It’s just drop cent by cent..

And then, i just ussage power AC and the battery is still not connect to my laptop up today~

Sorry my grammar is bad~

Thanks

On March 13, 2012 at 2:16am
Shannon wrote:

I have just brought a new charger for my Toshiba laptop to replace an old one that had a wire exposed and damaged. The new charger is supplying the correct voltage and turns my computer on and displays 0% available (plugged in,not charging)
Is there power surge protectors installed to avoid damaging your battery or computer hardware on toshiba laptops?
Could the damaged wire have caused a problem with the battery or with my laptop itself ?

On March 18, 2012 at 6:21am
KAILASH wrote:

I have laptop about 2 years old that is Compact professional 610, in which the battery is not taking back up for single second due to sort by high voltage but i can use it during the electricity is available.

Kindly suggest me what should i do or option

On April 19, 2012 at 8:59pm
Moinul Hasan wrote:

I Have rebuild my compaq C700 laptop but its not charging. After few debug i have found that the problem is on the circuit of the battery. is there any way to over come the problem? I found ur blog helpful. If i get any solution to redirect the charging option or any technique to redirect the connection.

On April 21, 2012 at 2:23pm
wale jones wrote:

this is nice

On April 25, 2012 at 5:08am
SN wrote:

Hi, my old battery is BTP-ARJ1 and it was dead.then i bought new one.but it is not charging more than 2% it says plugged in,not charging.so I replace my old battery’s circuit with new one.now the battery is charging but it says “consider replacing battery” same as my old one.is there anything i can do with this.

On April 25, 2012 at 1:39pm
robert leiker wrote:

lots of good info love it