A look inside the world of batteries

17May 2018

I googled the question “ should I charge my phone to 100”. Google returned 467 million results. From folks offering opinions on “how to properly charge” to others calling on “science”, there seems no obvious consensus in the media. Yet,  unlike views on more socially charged topics, this question ought to be a lot simpler and ought to have a clear cut answer. Let’s explore.

I start with an easy experiment. Take two batteries. Charge one of them continuously to 100% and discharge it back to zero. Repeat. Take the second battery and charge it only to 90%. Discharge it. Repeat. Now compare the two batteries.  Are there differences? the answer is yes, there is difference. The battery that was charged to 100% will age considerably faster. 

What do I mean by aging? The technical term is “cycle life.” In practice, it means that the battery charged to 100% will lose its ability to store electric charge faster than the other battery. The difference between the two batteries can vary between 100 and 300 charge cycles.

So is that good? Well, it depends on what your use is. The definition of “good” is relative.

For a smartphone, my answer is “I really don’t care.” 

For an electric vehicle, my answer is “yes, it is better, but may be only marginally.”

For energy storage batteries used by electric utilities, my answer is “yes, absolutely.”

Now, let’s dive into the details.

A smartphone battery usually lives about 500 to 800 cycles. By cycles, I mean the number of times you will be able to charge it (to 100%) and discharge it before it becomes old and useless. Some smartphone manufacturers do better than others. Apple’s and Samsung’s batteries tend to be closer to 500 cycles. Others like LG, Sony and Huawei tend to be closer to 800 cycles. 

Let’s convert cycles to real-life years. Most smartphones are charged once a day. So 800 cycles is about 2 years of use before your battery becomes old. That corresponds well with the average time for consumers to upgrade. But wait, you might say you plan to keep your smartphone for longer than 2 years. What should you do?

Naturally, one option is to spend $30 to $50 once your battery is depleted and get your phone serviced after 2 years. The other option is to charge your phone to only 80% or 90% instead of 100%. That exercise will probably get you an extra year of usage.

But that is not the only way to get more longevity. You probably don’t know that if you use a small AC adapter instead of a bigger one, you will probably get the same benefit. For this method, look for an AC adapter that is rated 5 Watts, or use the USB port in your PC to charge you handset. And that applies to iPhones or Android phones. What do you give up? You are giving up fast charging. If you charge your handset overnight, then you really don’t care.

A self-serving plug for Qnovo: Smartphones with intelligent charging algorithms will take care of longevity issues for you so you really don’t have to think about this question and its answer. 

Now, let’s talk about electric vehicles. Should you top off the battery in your electric vehicle (EV)? First, it is important to know that EV manufacturers (from GM and Tesla to Nissan and VW) already limit the charging of the car battery to somewhere near 80%. The 100% that you read in your dashboard is actually 80% of the what the battery is rated for. That figure usually is sufficient to meet the warranty terms of the vehicle, often 100,000 miles or 10 years.

If you are leasing your car, then you really don’t care. Your lease will expire long before any meaningful battery aging sets in. But if you purchased your EV and plan to keep for a long time, then you may have an incentive to not top off your battery.

But wait, that is also not the only way to get more longevity. Every time you use a supercharger or DC fast-charging, you are causing serious damage to the battery. So instead, try to avoid using superchargers. This is particularly acute for the Panasonic batteries used in some of the Tesla models.

Lastly, I will add a few final words about electric utilities and batteries they use. These are complex systems that are slated to operate for at least 20 years! They are also very expensive assets that cost millions of dollars. So longevity is a serious matter. Naturally, users have no say in how these batteries get charged. Utilities and battery manufacturers do watch over these batteries so that they can last for a long time.

18Apr 2018

5G is the evolution of the present LTE wireless network that carriers are beginning to deploy later this year. 

Yes, it will be a Global network, with every geography around the globe utilizing it at some point in the future. 

Yes, it will have Great capabilities, from streaming videos with very little if any delay, and seamlessly handle a large number of connected devices such as sensors.

Yes, it will Galvanize a new set of applications that may have not even been conceived of yet. Just imagine what the previous generations did to promote social networks, video, and other such uses that were not possible a decade ago.

Yes, it will have Grave consequences on the battery. The demands that the network places on the devices, in particular, the handset or smartphone, are significant. Early results show that the power consumption in the chipsets that run smartphones are higher by as much as 25 to 50%.

Yes, the effort will be Grueling to improve the battery’s performance and safety.

Much has been written about 5G and its planned deployment. Unfortunately, the coverage tends to be centered on the benefits of 5G and neglects the impact on the battery. If anything, it can be misleading in promising a longer battery life, contrary to the present data.

The figure below (courtesy of Verizon Wireless) highlights three main thrusts of 5G. At the low frequency bands, typically between 600 MHz and 900 MHz, 5G will continue to provide mobile broadband, similar to 4G / LTE connectivity on your smartphone or handset device. At these frequencies, the network will be limited by physics to maximum data bandwidths on the order of a few hundred Mbits per second.

 

 

5G introduces a new set of frequency bands that will go as high as 6 GHz where data rates can reach one or more Gbits per second. These higher data rates will provide new services that have much faster connectivity, or as Verizon Wireless calls it, enhanced Mobile Broadband.

The last frequency tranche is above 24 GHz where data rates can now reach 10 Gbits per second or higher.

There are three key observations to make here in relation to the battery. 

First, there will be a substantial increase in the amount of data traffic with 5G. Each bit of data consumes a small amount of battery charge. While electronics are getting incrementally more efficient in power usage, this efficiency is no match to the massive increase in data traffic, anticipated to be 1,000X higher than present-day volumes. This, unquestionably, will be the first strain on the battery requirements necessitating higher battery capacities and energy densities.

The second observation is more subtle but potentially more potent. The 5G networks provide new applications that are time and mission critical with a very low latency. In other words, the time that it takes the data to make a round trip from one device to another, and back to the original device (what engineers call latency) will decrease from a present-day value near 100 ms (milliseconds) to less than 10 ms. 

Who cares, you might ask! Imagine two autonomous vehicles on the highway traveling at 65 mph (105 km/h). In 10 ms, the vehicle would have traveled nearly one foot (about 30 cm). In 100 ms, the distance is ten feet or nearly three meters. This is the difference between avoiding a collision or a potentially tragic accident. 

But low latency means that the apps processor (or CPU) will be getting far less idle time that it does today. You see, battery-operated devices rely on the electronics being asleep (not drawing power) for a good portion of the time in order to save battery. So when the processor needs to be awake a longer duration of time, it will have a substantial impact on power consumption, and consequently the battery. 

The third and last observation relates to the new higher frequency bands at 3 – 6 GHz and greater than 24 GHz. Physics tell us that power consumption increases linearly with frequency. So just by going from the 900 MHz band to the 6 GHz band will incur up to 5X increase in power. 

Additionally, waves at these frequencies do not travel very far and tend to be greatly attenuated by physical obstacles like buildings and trees. This limited propagation requires that network carriers (like AT&T and Verizon) install far more antennas more densely. This large capital outlay will most certainly take time. Consequently, handsets operating at higher frequencies will most certainly need to increase the transmission power to overcome the attenuation. Once again, the battery suffers.

Of course, it is fair to expect that the power utilization in 5G networks will improve over time and manufacturers will derive improvements in efficiency. However, it is highly unlikely that 5G power requirements and impact on battery will be similar to those of 4G/LTE. The demands on the battery are certain to increase and put more constraints on battery performance and safety.

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.

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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.