A look inside the world of batteries

24Dec 2017

If Tesla Motors reduced the power of their flagship Tesla electric vehicles after, say, 50,000 miles of driving, the world would be up in arms. If General Motors throttled the Corvette engine to 4 cylinders after some number of miles, the government would probably be investigating. So why is it that when Apple throttles back the processors on their iPhones, we scratch our heads and don’t take Apple to task?

Apple is throttling the processors to preserve battery life. That is a fact admitted by Apple itself. Consumers have complained about premature shutdowns in older iPhones with aged batteries. Understanding the reasons behind such behavior is the topic of this last post of 2017.

I start by explaining a fundamental property of a battery: its voltage curve. The voltage curve is the relationship between the voltage of the battery and the amount  or rather percentage of electrical charge stored within the battery (naturally, 100% means full and zero means empty). You, as a user, get to see the gauge reading of the remaining charge in your battery, but not the voltage. We care about both values (charge and voltage) because either one of them can cause your smartphone to shut down.

So let’s dig a little deeper in the first figure below and understand how charge and voltage are related. It is the voltage curve for a fresh (unused) battery with nothing connected to its terminals. This curve is what engineers call the open-circuit voltage, i.e., no electrical current is flowing. One will notice that as the battery goes from full (far left) to empty (far right), the voltage gradually drops until it reaches a “cliff.” This behavior is characteristic of lithium-ion batteries. You will notice that the voltage is very low when the battery is empty.



Now let’s examine what happens to this curve when the smartphone electronics are connected to the battery. Engineers call this situation “under load” because the battery is now powering the electronics inside your mobile device, and electrical current flows through the battery. The next figure below shows that, in this scenario, the voltage curve actually shifts down. You will still notice that, however, the general shape of the voltage does not change much. The only change is that the voltage is now a little lower. The larger the current (the load), the larger the shift. A small change in voltage is ok, but as we will discover a little later, a large drop in voltage is not ok.



I will digress a little here to explain this drop in voltage. For that, we need to recall some high-school physics: Ohm’s law. When electrical current flows through the battery, the actually voltage is reduced by an amount equal to the electrical current multiplied by the battery resistance.

Two key observations to make here based on Ohm’s law:

  • A higher internal battery resistance results in a larger voltage drop;
  • A larger electrical current (to power the smartphone electronics and screen) also results in a larger voltage drop.

This may sound complicated if you don’t remember your high-school physics, but please bear with me. All you need to remember so far is that the battery has an internal resistance. A fresh battery has a small resistance. An old battery has a larger resistance. A faster processor and bigger display mean more current to power the device.

Therefore, as the battery ages, the voltage curve shifts down more and more — precisely what the figure below shows — until something really bad happens. The voltage of the battery is so low that it can no longer operate the electronics of your smartphone especially under peak conditions when the processor or the radio electronics need more power . The red curve below is for an old Apple iPhone 6 battery after 600 charge-discharge cycles. One can see it is now substantially lower than the voltage curve of a fresh battery. This now spells trouble because the low battery voltage may not adequately operate the electronics.



No we get to the crucial part: how does this relate to Apple’s throttling back their iPhones.

Most smartphone electronics, in particular the radio and wireless components, cannot operate when the voltage drops below 3.3 or 3.4 V. If the battery voltage does drop too low, the smartphone actually shuts down prematurely.

Let’s illustrate that point further in the next chart. The dashed green line is at at 3.35 V (a reasonable intermediate point between 3.3 and 3.4 V). Let’s first focus on the black curve (that of a fresh battery). You will notice that the battery voltage reaches 3.35 V right at empty. That’s good. That’s exactly what we want our smartphone to do. We want it to shut down because there is no more charge left in the battery, which corresponds to the battery gauge reading zero percent.



But in an old iPhone 6 (red curve), that’s not what happens! Instead, the battery voltage is too low to power the smartphone electronics even when there is remaining charge in the battery.  It shows that an old iPhone 6 battery reaches the low voltage point with the battery still holding about 20% of its charge. That’s not good; it means that this iPhone will actually shut down prematurely while the battery gauge reads about 20%. This is what confuses consumers.

So far, I am hoping I have not lost you in this lengthy explanation, and that you recognize how an older battery loses its voltage, which leads to an early shutdown.

This is, in particular, an acute problem for Apple because Apple rates its iPhone batteries at 500 cycles. In other words, after 500 charge-discharge cycles (or about 1 ½ years), the iPhone battery has degraded sufficiently to exhibit the low-voltage problems described above.

Fortunately, many other smartphone makers choose to use batteries and solutions that extend the cycle life of the battery to 800 or even 1,000 cycles – or at least 2 years worth or more. Sony Xperia smartphones, for example, do provide batteries with cycle life that is substantially more than 500 cycles.

So why does Apple throttle back their old iPhones? When the iPhone processor is running at full speed, it can draw a significant electrical current from the battery. Remember that Ohm’s law is the product of the resistance and the current. So by throttling back the processor, the current draw is less and hence there is less voltage drop because of Ohm’s law. The net effect is avoidance of an early shut down at the expense of user experience! What Apple should do instead is to make sure that their iPhone batteries can deliver 800 or 1,000 cycles instead of 500 cycles. By the way, you will notice that iPad batteries are rated to 1,000 cycles which is why you don’t see old iPads suffering from the iPhone shutdown problem.

If you own an old iPhone and are experiencing a slowdown, please go to the Apple store and get your old battery replaced….or get yourself a new smartphone with a better battery.


UPDATE: On 28 December 2017, Apple published a letter to its customers offering to replace the batteries in older iPhone models that are out of warranty for $29 instead of the standard $79. Kudos to Apple for taking responsibility for this issue and standing by their customers.

29Nov 2017

Congratulations, you just purchased a new Tesla model S electric vehicle (EV). You also committed an extra $2,000 to install a level-2 charger on a wall in your spacious garage. A level-2 charger will deliver 6 kW of power at 240 V to charge your big car battery overnight. Better yet, you are even considering investing an additional $20,000 to install solar panels on your roof and live a life with zero carbon. You might be cringing by now and thinking: “Wow, this is for the rich, not me.

So let’s consider instead a more socially responsible scenario. You leased a much more affordable Chevy Bolt that promises to give you 200+ miles of electric driving. You don’t have a garage. Perhaps you live in a large city so your car may be parked on the street. You are scratching your head: “How will I charge my car battery?” You might be lucky to charge your car during the day at work instead of overnight at home. But what about the weekends? No quick and easy answer.

As the adoption of electric vehicles becomes more widespread especially in congested urban geographies, questions about the charging infrastructure become prominent. Tesla leads in the deployment of their Supercharger network with over 1,000 charging stations installed worldwide, especially near major transportation corridors and highways. But the Tesla fast charging network is not compatible with other electric vehicles. Imagine that you can refuel your present vehicle at only one brand of gas stations, say at Shell only but not Exxon. No practical!

The buildup over the coming decade of a charging infrastructure that is publicly available to all electric vehicles is a must if EVs are to become a real alternative to vehicles powered by gasoline (or diesel). A fundamental requirement for charging is the availability of fast charging, more specifically, charging that can provide at least half-a-tank (or ¾ of a tank) in about 10 minutes.

Let’s do some simple math. An electric vehicle with a 200-mile range equates to a battery size of approximately 60 kWh. Half-a-tank is 30 kWh (or 100 miles). Charging 30 kWh in 10 minutes equals to 180 kW (or 3C effective rate). By the time we factor inefficiencies, the charging station needs to deliver a minimum of 200 kW. To put that in perspective, that is the amount of power used by an entire residential block! These chargers are big, expensive and hence have to be shared among dozens if not hundreds of vehicles.

But the infrastructure for fast charging is only half the problem. The elephant in the room remains: Can the battery itself charge at such a fast rate without being damaged?

The data suggest otherwise for the time being, unless we add a lot more intelligence to how we charge the battery.

The following chart shows the results of charging a battery at a slow rate compared to fast charging the same battery 30% of the time (or about once every three days) and 50% of the time (every other day).

The green curve shows how the battery retains its charge with slow charging. After 700 charge cycles (or about 130,000 miles of driving), it still retains 90% of its original charge. In other words, you can still drive 180 miles in what used to be a driving range of 200 miles. That is good!

The blue curve shows what happens if you charge 30% of the time. The capacity retention drops to 80% after 600 charge cycles. That is a rapid degradation. After 100,000 miles, your driving range is now 160 miles. It might be acceptable to some EV buyers but just barely. The resale value of your car has depreciated substantially below the average value.

The red curve spells major trouble. If you fast charge your electric vehicle every other day, your battery capacity drops to 75% of its original charge after only 300 cycles. That means that your driving range drops from 200 miles to 150 miles after about 50,000 miles of driving. What this graph does not show is that this battery is failing rapidly and has now become a serious safety hazard because of the presence of lithium metal plating. This is a serious problem!

So, if you own an electric vehicle such as a Tesla, and you are tempted to use the Supercharger network frequently, consider an alternative charging solution !!

04Oct 2017

Late summer is the season of new smartphones. Apple, Google, Samsung, LG are only a few names that announce their best ever devices in September. By now, you have all heard of or seen the new iPhones including the iPhone X, the beautiful Galaxy Note 8, the highly acclaimed LG V30, and today, the new Google Pixel 2 family. The Internet abounds with device reviews so this post will stay focused on their batteries.

Let’s start by comparing the batteries from this year’s devices to their kins from last year. The capacity figures (the mAh) vary up or down a little. For example the iPhone 8 and 8 Plus lose a few mAh compared to the iPhone 7 and 7 Plus but nothing significant. The Galaxy Note 8 sports a slightly smaller battery. LG adds a little extra capacity to the V30. By and large, it would be fair to say that battery capacities have not changed significantly from 2016 to 2017. Modest improvements in power consumption most likely contributed to maintain the status quo in battery capacity.

The other visible trend is that 6-in devices continue to use capacities in the range of 3,200 to 3,500 mAh, while their smaller 5-in brethren are using batteries with capacities near 2,700 mAh. It is not a surprise that the larger devices show a better battery life lasting one day or even longer. The iPhones 7 and 8 continue to lag with reviews complaining of less-than-standard battery life.

But not all is good news. The third trend is increasing pixel resolution and density. Full HD displays (1080 x 1920 pixels) are giving way to displays with much higher pixel count, pixel density and color experience. The Galaxy Note 8 exhibits the largest pixel count at 1440 x 2960 closely followed by the LG V30 and the Pixel 2XL which was manufactured by LG for Google. These larger and richer displays do consume more power and they will strain the battery’s capability to last all day. It is true that the new OLED displays are somewhat more efficient than LCDs but size and pixel count remain the dominant factors in the power equation. Expect that trend to continue well into 2018 causing the smartphone manufacturers to consider batteries with higher capacities while still maintaining slim designs.

The Galaxy Note 8, the LG V30 and the iPhone X gave us this summer a vignette of the future: Rich edge-to-edge displays with unmatched computational capabilities all embedded in very elegant and thin designs. That spells one thing: The battery challenge will not abate any time soon.

31Aug 2017

We proudly announced today that the new LG flagship smartphone, the LG V30, includes Qnovo’s adaptive charging technology. The V30 uses Qnovo’s QNI solution, our most sophisticated algorithms to manage its lithium-ion battery. In this post, we open our doors to give our readers insight to our technology and QNI in particular.

As complex and exotic as the battery may seem, you, the consumer, care only about a handful of things.

First, will the battery last you a whole day of use, no marketing gimmicks?

Second, will it charge fast enough? You don’t need blink-of-an-eye-charging but you don’t want to wait long too.

Third, will it last you at least two years or more, given that you are paying a premium price?

And lastly, can you rely that it will not risk your safety and the safety of those around you?

These attributes collectively define your overall battery experience; not one of them, but all of them together.

To last you a full day, the battery must have plenty of charge capacity, i.e., a lot of mAh. This is equal to a range between 3,000 to 3,500 mAh for today’s crop of smartphones. Anything more than that will make the smartphone unwieldy or too thick. To fit a 3,000 mAh battery in the small physical space inside a smartphone means high energy density. Today’s state of the art is near 650 Wh/l operating at a maximum voltage of 4.4 V. That’s the first headache already. At this high voltage and high energy density, the battery is really not happy and needs a lot of caring. I mean a lot of caring!

Fast charging the battery amplifies all the concerns of high voltage and high energy density, and makes them a lot worse. And if you have to charge more than once a day, well, this battery will need even more caring.

High energy density, high voltage and fast charging together are the factors that make the battery fail before two years, and risk making your battery unsafe.

Therein lies the challenge. How do we care for the battery ? and why has this required level of care become so much more sophisticated than ever before ?

As the old adage goes, “You can’t fix what you can’t measure.”

This leads to an important and critical new concept for batteries: Measuring what is happening within the battery, all the time, in real time, and then deciding what to do. By “within” I mean the “chemistry” that is taking place inside the battery…the stuff that you don’t see. This is called, in engineering terms, closed-loop feedback. Engineers know it, study it, and use it in countless situations.

Qnovo’s software adapts to your smartphone a measurement technique widely used in battery laboratories. It is called electrochemical impedance spectroscopy (abbreviated as EIS). It helps our scientists understand what happens inside the battery without destroying it. Qnovo’s innovation is in implementing EIS in your smartphone so that it is always monitoring your battery’s internal chemical processes.

We announced earlier this year that the Qualcomm® Snapdragon 835 that powers the LG V30 includes hardware that accelerates Qnovo’s algorithms. Indeed, the additional hardware in the Qualcomm Snapdragon 835 chipset extends the utility of EIS inside the smartphone. The hardware in this new chipset enables measurements and frequencies that were not available in older chipsets. Qnovo’s QNI software takes advantage of this new hardware to gain deeper insight into the battery, again all in real time.

Now we get to the second portion of closed loop: What to do after making a measurement. As it turns out, and we thank science for that, charging the battery is a powerful knob to alter and affect what happens inside the battery. Qnovo’s adaptive charging takes the information from the EIS measurement, and then adjusts the charging current to reduce and mitigate possible harmful reactions detected during previous measurements.

With QNI, this “closed loop” happens a lot faster than its sister software product, QNS. As a result, it is able to detect more potential problems and react appropriately. Throughout a single charge, QNS makes approximately 200 measurements on the battery, whereas QNI makes close to 20,000 measurements.

Over the past years, we have collected a gigantic database of measurements on batteries from the vast majority of battery manufacturers. We have tested large quantities of batteries under diverse and extreme conditions. This knowledge allows Qnovo to train our algorithms to make them more efficient and more accurate especially as battery materials continue to evolve.

The skeptic might ask, “Great, but how does it help me, the end user?”

The most important benefit that the user derives is the health of the battery. You get a healthy battery AND more capacity AND fast charging…in other words, the consumer gets a great battery experience encompassing the attributes mentioned at the beginning of this post.

You, the consumer, do not have to worry whether your usage might hurt the battery. You don’t have to worry about fast charging because it might damage the battery. You don’t have to worry about charging to less than full because it helps the battery’s longevity. None of these should be your concerns and none should keep you thinking about the battery. Qnovo’s adaptive charging takes care of these battery issues in the background, and gives you a healthy battery with the best user experience.

So, if you are in the market for a new smartphone, do consider an LG V30 and do enjoy its battery experience.

16Aug 2017

School started this week for most of us so it is time to resume the posts. Today’s post continues with insight into the subtleties of the lithium-ion battery. It is surprising how a simple device, with only two contacts, can be so intriguing and complex.

As summer nears to an end, several smartphone makers ready their newest and greatest devices for launch. Samsung announces their Note 8 on 23 August. LG is announcing their flagship V30 a week later. And we are not forgetting Apple as they ready their newest iPhones in September.

All of these new devices will come with amazingly beautiful and large displays, top-of-the-line processors and of course, batteries to power them. At an expected price point in excess of $700, consumers are keeping their smartphones for two or even three years. So will their batteries last that long?

We will examine here one of the parameters that impact the longevity of the battery…and give you some tidbits on what you can do to keep your battery fresh for longer than average. Today’s post is on voltage. Voltage is the alt-nature to state-of-charge (SOC). This is very much the principle of operation of the fuel gauge — how you get to read at the top of your screen the percentage of remaining battery life.

When I say voltage, I mean the maximum voltage that the battery will see. It also determines the maximum available capacity in mAh. Look at the label of a battery and you will observe a maximum voltage during charge and maximum capacity for that battery. Most state-of-the-art batteries operate at a maximum voltage around 4.35 V or 4.4 V. This is also the voltage that corresponds to a 100% battery reading.

If you choose to charge your smartphone to a lesser percentage, say to only 90%, then the battery voltage stops at a lower value. For a battery that is rated 4.35 V, 100% corresponds to 4.35 V. At 95%, the voltage is 4.30 V. And at 90%, the voltage is 4.25 V. These are small differences in voltage values, but significant differences in capacity.

Let’s take a particular example with a battery having a maximum capacity of 3,100 mAh at 4.35 V. Therefore, at 4.25 V, the maximum available capacity becomes a little over 2,800 mAh.

You are now wondering: why would anyone want to do that?

The answer is: Battery longevity. If you don’t have the best battery, or your smartphone manufacturer is not putting the best battery management intelligence on your device, then you ought to be very concerned whether your battery will last you more than one year. Battery issues after 6 months or one year are a significant cause for warranty returns.

Let’s back it up with some measured data.

The following chart shows the maximum available capacity for a battery rated at 3,100 mAh at 4.35 V. At this voltage, this battery will only last about 400 cycles, or about a year. You will complain about the loss of use much before that.  The brown line shows that your battery has lost 250 mAh of capacity after 6 months….that’s about 2 hours of use time. Ouch!


Now, let’s look at the case where the smartphone is charged to only 95%. That is a maximum available capacity of 3,000 mAh instead of 3,100 mAh. Now follow the dark green curve in the chart. It fades at a much slower rate than the brown line. In fact, it crosses over the brown line at about 300 cycles, or about 10 months. In other words, after 10 months, it offers more capacity. This illustrates the tradeoff between voltage and longevity.

A smartphone maker who has implemented advanced intelligence on their battery (like Qnovo’s) will not suffer from this ailment. But if you suspect that your device does not have such intelligence, then you will do yourself a big favor by charging your battery to a maximum of 95% or even lower if you can.