BU-603: How to Calibrate a “Smart” Battery

Learn why calibration is needed and how often it is required.

When designing a fuel gauge, engineers commonly make a misjudgement by assuming that a battery will always stay young. As with people, batteries age and the changing characteristics must be taken into account to maintain accuracy. Fancy fuel gauges can provide a false sense of security in believing that the displayed battery readings are correct. For the casual user of a mobile phone or laptop, a fuel gauge error is only a mild irritant, but the problem escalates with medical and military devices, as well as drones and electric drivetrains that depend on precise range predictions.

The chemical battery representing the actual energy storage remains the master while the digital battery provides peripheral support by relying on the information obtained from charge and discharge cycles. But like all fine machines, precise settings begin to shift and need adjustment. The same happens with an SMBus battery that also require periodic calibration. The instructions for an Apple iPad reads: “For proper reporting of SoC, be sure to go through at least one full charge/discharge cycle per month.”

Figure 1 demonstrates a digital battery that is drifting away from the chemical battery; calibration corrects the tracking error. The accumulating error is application related and the drift on the chart is accentuated for effect.

battery as a function of time

Figure 1: Tracking of Electrochemical and digital battery as a function of time. With use and time the electro-chemical and digital battery drift apart; calibration corrects the error.

Note: The accumulating error is application related; the values on the chart are accentuated.

A smart battery self-calibrates by taking advantage of occasional full discharges, but in real life this seldom happens. Most discharges are intermittent and go to random depth. In addition, the load signatures often consist of high frequency pulses that are difficult to capture. The partially discharged battery may be partly recharged and then stored in a warm room, causing elevated self-discharge that cannot be tracked. These anomalies add to the display error that amplifies with use and time.

To maintain accuracy, a smart battery should periodically be calibrated by running the pack down in the device until “Low Battery” appears and then apply a recharge. The full discharge sets the discharge flag and the full charge establishes the charge flag. A linear line forms between these two anchor points that allow SoC estimation. In time, this line gets blurred again and the battery requires recalibration. Figure 2 illustrates the full-discharge and full-charge flags.

Full-discharge and full-charge flags

Figure 2: Full-discharge and full-charge flags. Calibration occurs by applying a full charge, discharge and charge. This is done in the equipment or with a battery analyzer as part of battery maintenance.

Courtesy Cadex

Battery analyzers serve as a valuable tool to calibrate a smart battery. An analyzer fully charges the battery and then applies a controlled discharge that provides the all-important capacity readings of the chemical battery. This discharge measurement is a truer reading than what coulomb counting provides by capturing past discharge events of the digital battery.

How often should a battery be calibrated? The answer depends on the application. For a battery that is in continued use, a calibration should be done once every 3 months or after 40 partial cycles. If the portable device applies a periodic full deep discharge on its own accord, then no additional calibration should be needed.

What happens if the battery is not calibrated regularly? Can such a battery be used with confidence? Most smart battery chargers obey the dictates of the chemical battery rather than the digital battery and there are no safety concerns. The battery should function normally, but the digital readout may become unreliable.

Some smart batteries feature impedance tracking. This is a self-learning algorithm that reduces or eliminates the need to calibrate. If calibration is required, however, several cycles instead of only one may be needed to achieve the same result as with a standard system.

Max Error

The accuracy between the chemical and digital battery is measured by the Max Error. Max Error stands for “maximum error” and is presented in percentage. A low reading indicates good accuracy, and as the precision diminishes with partial cycles, the Max Error number increases steadily. This supervisory watchdog can be compared to a medical doctor who measures a medical condition by a number.

Some manufacturers recommend calibration at a Max Error of 8 percent; readings above 12 percent may trigger an alarm and 16 could render the battery unserviceable. No unified standard exists to determine what Max Error level requires service or what constitutes an error; every battery manufacturer follows its own recommendation.

Screen Capture

The SMBus system provides a wealth of information that includes battery manufacturing date, battery model and serial number, capacity, temperature and estimated runtime, as well as voltages down to the cell levels. It is an engineer’s delight to have all this data in a table, but the fine print may confuse the user more than providing help. A busy nurse in a hospital, the policeman on duty and the solider in combat has only one question: “Will the battery last for my mission?” Figure 3 illustrates a screenshot of the data stored in an SMBus battery.

SMBus battery

Figure 3: Uinversal screenshot of SMBus battery. Data is organized in tables to assist analysis, a format that is less suited for the everyday battery user. Access is by a software tool.
Source: Texas Instrument

Of special interest in terms of battery state-of-health (SoH) is full charge capacity (FCC), coulomb count that is hidden in the table among tons of other information. FCC can be used with reasonable accuracy to estimate battery SoH without applying a full discharge cycle to measure capacity. Best accuracies are achieved if the battery is being cycled with a full charge and an occasional deep discharge. If used sporadically, a deliberate calibration involving a full discharge/charge cycle will be needed from time-to-time to maintain accuracy.

Last updated 2016-09-02

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Comments (44)

On March 9, 2011 at 4:40am
Bakhtawar Gul wrote:

Thanks for these lessons, it will be highly appreciated if you kindly covert these lesson in pdf format for downloading the whole document….....

On July 22, 2011 at 12:58am
saad wrote:

dear sir ,

how i can calculate the 50 % of battery life and how i now the battery voltage when i get the 50 %

On September 5, 2011 at 10:15pm
Lydia wrote:

When applying “Full Discharge”, should we discharge battery to 0% ?
Figure 1. shows 10%. Is it means that we should start to charge battery after battery is discharged to 10% ?

On January 2, 2012 at 6:48pm
Yuttana wrote:

Can this calibration apply to lead-acid battery?

On March 11, 2012 at 11:23am
Lindsay wrote:

I have two batteries for my Canon 50d camera.  The Canon battery seems to work just fine.  The other is an aftermarket battery.  It has worked fine for about 2 years, but two days ago I charged it in anticipation of taking a number of photos yesterday.  At the start of the day I put the aftermarket battery into my camera and the camera showed it as discharged.  The original Canon battery performed for the day.

The aftermarket battery showed as completely charged when I put it on the charger at home, and checking with a simple volt meter showed a voltage of 7.4 - 8 volts.

Is there some sort of circuitry that is forcing the camera to no longer recognize this aftermarket battery?  Am I doing something wrong?  Does the camera or battery need to be ‘reset’?

Thanks for any assistance you can provide.


On April 8, 2012 at 5:48pm
khalil wrote:

if the battery is not calibrated, it may slow down my laptop ?

On September 22, 2012 at 10:57pm
mahabubur rashid wrote:

the article will help me to sustain making quality batteries. I will ever great full to you & battery university.

On December 9, 2012 at 10:01pm
steve h wrote:

If “calibration should be done once every three months or after 40 partial cycles”, then would this not lessen the charge cycles of a Li-Ion cell?  Full depletion of a Li-Ion will do more harm than good to the lifespan of the battery, will it not?

On December 17, 2012 at 3:58pm
Tim wrote:

@Steve H. Battery’s have a limited cycling. As you said full depletion of the battery will hurt the battery, but the Li-Ion cell reserves enough charge from sustaining permanent damage. Whether you keep it in storage or not calibrate it all, it will still degrade over time. So to save yourself from increasing your risk in losing data or your device not showing proper percentage of charge… Calibration is fine if you don’t do it often. Just think of it as going through 1 complete cycle when you do the calibration.

On December 30, 2012 at 5:44am
John Manning wrote:

Thanks 4 all the tips on how 2 Maximize Laptop Batteries

On December 30, 2012 at 1:00pm
Bart wrote:

@Tim: But this article says:
“(...) until the battery is fully depleted and “Low Battery” appears”
which means, that the full depletion, when device won’t start up, is not necessary - the battery is fully-discharged since low battery notification appears (at 10% charge?). Please correct me if I’m wrong.

On December 30, 2012 at 1:38pm
Tim wrote:

@Bart Full depletion as in the device won’t start anymore. For example, charging your phone to 100% then run it down until the device shuts itself off. That’s a full depletion cycle. Look over at other manufacturers recommendation, such as… http://support.apple.com/kb/HT1490 They also recommend doing this procedure. So, yes you would need to run it down until it totally shuts off. That’s the only way it will be able to set the appropriate flag.

If you haven’t calibrated from 100% to full depletion then the gauge wouldn’t know what charge it would be at. That’s the point of having this calibration, so that it sets the flag at the lowest and highest flag point of being full.

On December 30, 2012 at 1:43pm
Tim wrote:

@Bart In addition to my response to you. Always follow per manufactures recommendation if present. For example, the new Apple Macbook with the non-removable battery has already been calibrated from factory and does not need this procedure. I do not know the reason so I cannot answer that question, but only to postulate that they are using a different method to gauge the remaining charge of the battery. If anyone has information and link to the source it would be greatly appreciated.

On December 30, 2012 at 4:52pm
Bart wrote:

@Tim: Thank you so much for your valuable information. Everything is clear now (except Apple’s non-removable battery, so I would also appreciate if someone could post any details).

On January 9, 2013 at 11:00pm
Kevin wrote:

@Tim Once I go from 100% to the full-discharge flag (drained iPhone until it shuts off), do I need to fully charge to 100% without unplugging from power source to complete the process? Apple’s website does not specify that you need to wait until it’s 100% after you discharge it to calibrate.


On January 10, 2013 at 5:48am
Tim wrote:

@Kevin Yes you would need to charge it right back up to 100%. Logic is still the same in terms of setting the low flag(most depleted point) and charging it to the 100% mark thereby setting the full flag.

As quoted by their webpage:
“Be sure to go through at least one charge cycle per month (charging the battery to 100% and then completely running it down).”

One charge cycle still means to charge the device back up. If you run it down and not complete the charge, your efforts would be for nothing.

On January 10, 2013 at 8:58am
Kevin wrote:

@Tim That’s what I figured, but wanted verification. Thanks for all the valuable information!

On January 10, 2013 at 11:18am
@Kevin wrote:

no problem smile

On February 2, 2013 at 2:49pm
Potato wrote:

But why does the red flag on the diagram appear at 10%? Does the battery really need to reach 0% or anywhere below 11%?

On February 9, 2013 at 2:52pm
Clintz wrote:

@KEVIN I did my first charge cycle with open all apps,turn the brightness into full,notifications on etc..

Am i right or i did it wrong?i mean it’s ok to do charge cycle while all my apps was open etc?

On February 23, 2013 at 5:57pm
Tim wrote:

@Kevin If you read here: http://batteryuniversity.com/learn/article/low_voltage_cut_off

You’ll see that lithium ion batteries in nature have a protection circuit to protect the battery from overly discharged. The graph that you see from what I gather is the cut-off of the batteries capacity. So in sense when your device states it has nearly reached 0% that means it hit the cut-off or at least close to it.

You can however hit the “True” 0% capacity of your lithium ion battery, but if you read the article on here that I provided for you… You’ll see that you are going to prematurely damage the battery.

On April 29, 2013 at 8:11am
viva wrote:

i have a xperia ion and i caliberated by a different method . but still im having issues with my battery ...As soon as the battery reaches 45% it shows the message that 1% battery is left .i tried calibration again but it didnt help ...any suggestion

On June 7, 2013 at 8:41am
Manu wrote:

@viva May be there’s a problem with the software, try using 3rd party application or try flashing the phone.

On June 26, 2013 at 4:58am
garvit dahiya wrote:

this is a really good website. it tells almost everything one needs to know about a battery. i think that you should also include article and category about li-po battery used in RC systems.

On August 28, 2013 at 11:19am
Monaem Hossen Totul wrote:

From long time I’ve worked with battery & charger’s, in these period I used same battery’s in many ways. Result is different from them, and I learned battery life depends on it’s charge & discharge conditions. From that event I decided, I’ve to fix battery maintenance policy.

On May 6, 2014 at 1:27pm
hisanr wrote:

The most adequate method to do a full discharge (100% to a minimum of 3%) consists of the following procedure:

  Fully charge the battery to its maximum capacity (100%);

  Let the battery “rest” fully charged for 2 hours or more in order to cool down from the charging process. You may use the computer normally within this period;

  Unplug the power cord and set the computer to hibernate automatically at 5% as described by the image sequence below (click images to enlarge). If you cannot select 5%, then you should use the minimum value allowed, but never below 5%;

  Leave the computer discharging, non-stop, until it hibernates itself. You may use the computer normally within this period;

  When the computer shuts down completely, let it stay in the hibernation state for 5 hours or even more;

  Plug the computer to the A/C power to perform a full charge non-stop until its maximum capacity (100%). You may use the computer normally within this period.

After the calibration process, the reported wear level is usually higher than before. This is natural, since it now reports the true current capacity that the battery has to hold charge. Lithium Ion batteries have a limit amount of discharge cycles (generally 200 to 300 cycles) and they will retain less capacity over time.

Many people tend to think “If calibrating gives higher wear level, then it’s a bad thing”. This is wrong, because like said, the calibration is meant to have your battery report the true capacity it can hold, and it’s meant to avoid surprises like, for example, being in the middle of a presentation and suddenly the computer shuts down at 30% of charge.

On August 25, 2014 at 8:04am
lule ramzan wrote:

would like to know if deep cycle batteries when stored on concrete floors or metalic casing happen to have a problem of high discharge rate. Also inform me of any other storage problems.
thank you for the lessons.

On June 2, 2015 at 11:10pm
Ashton wrote:

So today on Jun 2nd (around 11pm-12am), my LG optimus L90 stopped charging at 97% and the charger plug was still plugged in, i was wondering if i needed a new battery or is there a way to fix it?

On July 12, 2015 at 2:41am
Mariana wrote:


Can you help me ...I have axperia z1 and the battery was finishing real fast. But now it came to 0% and dont charge any more… is there a way to give extra live so I can backup my pictures? Becouse I call the Sony but they told that I will loose all my information…


On September 6, 2015 at 10:35pm
Pete wrote:

Mariana - All modern phones (and other electronic items) use a type of internal memory called flash memory which will keep the information stored in it (ie your photos etc.) even when there is no battery connected or if the battery is fully discharged. You do not need to worry about losing your information but accessing it. Try to use the phone whilst the charger is connected. You should be able to transfer your data to either an SD card within the phone or possibly to a computer using software from the Sony website. If you transfer the data to an SD card you can then remove the card from the phone and copy the data on it to a computer using a card reader. With regard to your phone battery, if it won’t charge you probably need a new one. Just search on the web for ‘Xperia Z1 battery’ and you’ll find loads of retailers at reasonable prices. Don’t buy one from your phone service provider (eg Vodafone or O2 etc.) as their battery prices are a rip off.

On September 6, 2015 at 11:08pm
Pete wrote:

There seems to be some confusion with regards to the correct way to calibrate a Li-on battery due to the device low battery warning.
The low battery warning is purely implemented in the device software as a means to prevent possible data loss whilst using it and is completely independent of the battery management system.
Even if you let your device run until it shuts down automatically due to lack of battery charge the battery management system will still keep the battery charge at a high enough level to prevent damage to the battery pack.
The battery gauge that you see displayed on the screen is basically the amount of USEABLE charge the battery has and NOT the absolute total charge of the battery. This is why you can change the battery low warning to any percentage you choose - it’s not there to protect the battery (that’s done automatically by the battery management system) it’s there to give you enough time to save your work or connect the charger.
Therefore, if you intend to calibrate your device battery you need to let it run down past the warnings until it shuts down automatically BEFORE recharging, otherwise you may not discharge the battery sufficiently to register the battery management systems discharged flag, thus rendering your attempt to calibrate the battery incomplete.
Remember there are two different (but connected) systems at play, the battery management system, which monitors and controls the health of the battery and the software user interface (and associated power control software), which reads data from the former to display an indication of battery charge status and level and respond to various flags (like shut down when the discharge flag is set).

On September 8, 2015 at 4:26am
Mariana wrote:

Tks Pete! The solution that I found was sending the phone to Sony to change the battery because the battery run out of all power. But I send the 13 of July and I still didn’t receive it back and they told me that they will erase all information from the phone :(.

On September 8, 2015 at 5:44am
Pete wrote:

Sounds like a long time to wait! I don’t see why they need to erase your content from the phone if they’re just changing the battery. Maybe you should check the phones IMEI number against the one for your original phone when it comes back in case they just send you any phone of the same model! Hope you get it back soon. I’d chase them up if I were in your situation. Good luck.

On October 6, 2015 at 6:31pm
Brian Milne wrote:

I understand that when larger Lipol batteries are used in electric vehicles and the same cells in RV vehicles, off-grid etc, that balance boards are fitted across or between cells.
I have see such installations but I am unable;e to find out about these,  or from where these boards can be purchased.
Are you able to explain of their use and from where might these be purchased?

Many thanks for your time, Brian


On October 6, 2015 at 6:35pm
Brian Milne wrote:

Hi, With the larger lipol batteries as used on electric cars, RV vehicles and off-grid systems, balance boards are connected across the cells. Are you able to explain their use and from where these can be purchased?
To date I am unable to find anything on the net.

Thanks for your time, Brian

On October 26, 2015 at 1:47pm
Richard Uschold wrote:

I just bought a new battery for my 5 year old Galaxy S II. The new battery just barely holds a charge longer, which is under a day of light usage. I paid very little for the battery, so I’m not surprised it is not as good as a new one. I am surprised it is barely better than my five year old battery!

I have never calibrated my battery. I never heard of such a thing. This procedure seems rather similar to the memory effect of Ni-Cad batteries, though perhaps for a different reason.

1) Is the calibration logic strictly on the battery, the phone, or both?
2) The real issue: If i swap batteries in the phone that are calibrated differently, will the readings be all confused?



On February 27, 2016 at 2:07pm
Invictus wrote:

whether the li-ion battery memory property ?
should be charged , without waiting for discharge to zero ? how to prolong the li- ion battery ?

On July 25, 2016 at 10:08pm
Harmeet wrote:

Good articles but I don’t find any answers from author/site to the posted queries/responses.

Why leave the provision for comments if none are to be answered!

On April 22, 2017 at 2:38pm
Fred Gage wrote:

I just got a new (or refurbished) Li-ion Battery for my old mac powerbook 12” aluminum. The instructions say “please discharge the battery to 2% then charge fully to 100 %.
Since the battery came with no initial charge how can i discharge to 2%. I assume I will have to charge it to 100% and then discharge to 2%. Then finally charge it to 100%.
Could you tell me if this is correct. Also, is this figure (2%) written in the system prefs?Should I first reset all the numbers that pertain to the old battery or is this done automatically by calibrating the new battery?


On April 28, 2017 at 1:16am
nick wrote:

thanks for useful article

On January 10, 2018 at 2:29am
Benjamin wrote:

i repaired my laptop cells without doing what you said “keeping the battery alive” and now the battery isn’t in a position to power on my laptop but it has full potential. what can i do?

On April 15, 2018 at 4:16pm
Farouk wrote:

I have been using “Coconut Battery” to monitor both the charge and the capacity of my 2008 MacBook battery. What do readers think of “Coconut Battery” as a program for monitoting the state of health of the battery?

On April 26, 2018 at 3:29am
Joshua Wang wrote:


How does a BMS relate to all of this? If I have a battery pack, then add a BMS can it now be considered a smart battery?

Thanks in advance.

On November 16, 2018 at 10:26pm
Vicky wrote:

@tim sometimes my battery increases 2-3% by itself.should u calibrate it?thanx in advance