The Basics

28Sep 2014

No, it is not “Batteries Made Simple,” nor “Better Make Sense,” though BMS do indeed try to accomplish both in a very indirect and implicit way.

BMS stands for Battery Management Systems. These are electronic systems, both hardware and software, whose primary function is to control the operation of the battery. In order for batteries, and more specifically lithium-ion batteries, to deliver the requisite safe performance, they must operate within some very well defined, and in many cases, strict limits. For example, a lithium-ion battery cannot be charged above a certain voltage specified typically by the manufacturer in the range of 4.2V and 4.35V. Maximum current values and temperature limits are other examples. Failure to observe these limits will result at the very least in performance degradation, and quite likely in a seriously unsafe outcome such as fire or even death. A Chinese flight attendant died in 2013 while using her iPhone 5 during charging; her electrocution was attributed to a counterfeit charger she purchased in China.

BMS cover several functions including charging the battery, measuring the battery’s amount of stored charge, and making many decisions to ensure the battery remains within a safe operating mode. 

The fuel gauge, the device responsible for giving you the percentage of “battery full” in your mobile device, is an integral part of the BMS. Fuel gauges were practically inexistent until a startup company called Benchmarq introduced them in the early 1990s, initially for notebook PCs. Fuel gauge functionality is integrated today in the power management integrated circuits (known as PMIC) manufactured by companies such as Qualcomm and Texas Insruments, yet sadly, there has been very little if any meaningful innovation added since Benchmarq — I will resist the temptation of openly promoting Qnovo here. For example, the accuracy of the fuel gauge in your smartphone is quite poor, and can often be as high as 5 to 10 percentage points. Next time you look at your mobile device and it reads 20% battery remaining, keep in mind that may be as little as 10% or as high as 30%. Worse yet, device manufacturers routinely fail at translating this reading into a meaningful usage number like  hours of remaining use.

Battery charging is another function of the BMS. Yet charging remains extremely primitive. Most mobile devices today charge using a method called constant-current constant-voltage (abbr. CCCV) that was invented in the 19th century to charge lead-acid batteries. Its simplicity certainly made it irresistible; but there is no free lunch. CCCV charging has now been clearly established as a primary cause of battery damage. Next time you look at your mobile device and wonder why it is not lasting you a full day as it did when it was new, you can start by pointing the finger to CCCV charging. Yet, most mobile devices still stick with this archaic charging approach.

If you are a battery user, you also might want to see additional information such as the health of your battery. Nope! You can’t get it from present-day BMS in your mobile device. You may want to charge your mobile device faster. Nope! You can’t do it. You may want to know whether your battery may have been defective from the onset. Nope again! Both you and the device manufacturer are in the dark. Yes, you can walk today into the store of your favorite wireless carrier (or operator) and tell them that your battery was defective, and there is virtually little they can do to prove or disprove your concern. Insist a little and you will walk away with a replacement smartphone or mobile device. And while you are at it, let them know that you want more features such as faster charging!

This is the sad state of battery management today. It’s not because innovation is lacking or the technology is behind. Solutions do exist. Device manufacturers are slow to implement innovation. So let them know what you want!

27Sep 2014

Today’s post takes us on a brief journey inside a lithium-ion battery. What is its internal structure and how does it actually store electrical energy?

Let’s first start with a capacitor…the kind of stuff you studied in high school physics. It has two plates separated by an insulator, for example, an air gap, or may be a thin sheet of mica. If you recall your science experiments with a capacitor, it stored electrical energy because electric charge (electrons here) was pulled from one plate, traveled across an electric circuit and moved the opposing plate. This act of separating electric charge in the basic mechanism of energy storage. Its evidence in an electric circuit is the presence of a voltage across the two plates (or terminals) of the capacitor.

So why can’t we use an electric capacitor for energy storage? Simple…its energy density is way too small. But wait, you say, capacitors in our high-school physics classes were never described in terms of energy density. They were described in terms of capacitance measured in units of Farads.  No problem, we can use either methodology. Typical capacitors have capacitances ranging from a few picofarads (one pico is one trillionth) to may be millifarads (one milli is one thousandth). By comparison, a lithium-ion battery has an equivalent capacitance about one million times larger. 

So a rechargeable battery is fundamentally an electrical device for storing energy at the highest possible energy density — or in very simplistic terms, think of it as a capacitor whose two plates are separated from each other by only nanometers (one nano is one billionth). 

The internal structure of a lithium-ion battery is remarkably yet deceivingly simple. Much as a capacitor, it has two metal plates called electrodes. In lithium-ion batteries commonly used in mobile applications, one electrode is made of an alloy of lithium, cobalt and oxygen written colloquially as LCO. The other electrode is made of graphitic carbon, the kind of material you find in the lead of a pencil.

Now here’s the magic and beauty of operation. The lithium ions are present in a type of solution immersed between these two electrodes called electrolyte. When the battery is being charged, the lithium ions travel towards the carbon electrode, and physically enter the carbon matrix. The ions actually sit inside the carbon material. Think of swiss cheese and filling the empty spaces lithium ions. When the battery is discharged, the opposite happens and the lithium ions insert themselves inside the LCO electrode. Every time the ions go back and forth, energy is stored then returned. Very elegant. 

In real life, battery manufacturers build large sheets of electrodes, I mean very large, several feet wide and tens of yards in length, then assemble the sandwiched structure, then usually (though not always) roll it together in a cigar-like shape to make the device as compact as possible.

A photo showing the internal structure of a lithium-ion battery. Close examination shows the cigar-like roll containing the electrodes and the electrolyte. Courtesy of Dr. Venkat Srinivasan at the Lawrence Berkeley National Labs.

One last word on safety. Why are lithium-ion batteries prone to catching fire? It’s a complex process but let me explain with a simple example. Under some extreme conditions, say if we are carelessly charging the battery over its maximum allowed limits or creating a short-circuit by punching a nail into the battery, oxygen is released from the LCO electrode. But lithium is very reactive in the presence of oxygen and immediately catches fire. And lithium fire cannot be put out with water. Water actually makes the situation worse.

The good news is that lithium-ion batteries have gotten extremely safe over the past few years as battery manufacturers have made their designs less prone to these failure, and electronic protection systems ensure that the battery never sees extreme conditions.

20Sep 2014

Damage in a battery happens. You can’t stop it. It’s part of the physics. Yes, it is possible to mitigate it. It is possible to postpone its onset. It is possible to reduce its impact (that’s part of what our company Qnovo does)… But it’s always there and we need to deal with it. Battery manufacturers have tended to sweep this issue under the rug but it is now coming back to bite them hard.

In technical terms, this damage inside the battery is referred to in terms of “cycle life.” It is essentially a measure of how many times the battery can be charged and discharged before it is deemed dead. As I mentioned in the previous post, a battery is deemed dead when its maximum capacity reaches 80% of its original capacity as a fresh battery. So say a fresh battery has a maximum capacity of 2,500 mAh on its first day of use. After some number of charges and discharges, the internal damage reduces this maximum capacity. Eventually, this figure reaches 80% x 2,500 mAh = 2,000 mAh at which point it is officially deemed to be “dead”, i.e., it needs to be replaced.

Why 80%? and not 75% or 63.1849%? Because experience has shown that shortly past the 80%-mark, the damage accelerates rapidly and the battery capacity plummets very quickly. Not good!

But now you are saying, “how can I know?” Well, welcome to the world of opacity in how battery makers specify their products. As a consumer, you don’t know, nor you can measure it easily. Device makers tell you trust me, but you should not! All these apps that you can download from the Apple or Google stores also don’t tell you anything. Right now, sadly, the only way you can tell that your battery is dead or dying is because it feels that it is dying. Your battery can’t last you the day when only a few months earlier it did. Now to be sure, you also have to make sure that you don’t have one or more rogue apps draining the battery in the background. So if you reset or even restore your mobile device and its battery is still not delivering, then it is a fairly strong hint that something is very wrong with the battery. If you are asking “why can’t you fix it,” the answer is “we can and we are.” Let your mobile device manufacturer know that you are not happy if you suspect your battery cycle life is compromised.

Let’s get back to cycle life. As you can see, cycle life and battery capacity are very closely tied together. Capacity is effectively the capacity that you get on your first day of operation, and cycle life is a measure of longevity of your battery’s capacity. Cycle life is almost like the “Expiration Date” printed on a gallon of milk at the grocery store; except imagine that grocery stores decided one day to simply eliminate printing this crucial date. Grocery stores don’t dare do it! Well, many mobile device manufacturers choose to hide or not disclose the cycle life — effectively this expiration date of the battery is hidden. We are working on changing this behavior. But for now, I will give you some hints and tips on how to deal with this.

Most mobile devices including smartphones and tablets are rated to 500 cycles, i.e., you, the consumer, can expect to have 500 consecutive full charges and full discharges before your battery is deemed dead. Some devices do better than others. For example, older Apple iPhones lasted more than 500 cycles, whereas others either made 500 or fell shy of that figure. 

But some carriers (or operators are they are called outside the US), and in particular, Verizon Wireless, began demanding that mobile device manufacturers increase their cycle life specifications to 800 or more cycles, to effectively cover a 2-year warranty on the device. This new specification is beginning to proliferate but battery manufacturers are not happy! Increasing cycle life performance is not easy for them, and guess what, most of them are based in Asia and they don’t like to ask for help!

So one of the tricks that manufacturers do to increase cycle life is to — hold on to your seat — increase charge times! Ouch! Now, you are becoming increasing familiar with the battery whack-a-mole strategy that battery manufacturers follow. You want more capacity, well, you may get worse cycle life…you want better cycle life, well, you will get worse charge times….and so on.

Fortunately, the technology to fix this whack-a-mole problem already exists…mobile device manufacturers have to deploy it more universally. For now, here are some hints — albeit a little inconvenient — that you can apply to extend the cycle life of your life battery:

  • Charge your device slowly using the USB port on your PC or notebook, not wall charger or AC adapter. This effectively limits the charging current to 500 mA. Yes, it is slow, but if you are not in a rush, it will help your battery.
  • Charge at room temperature! Not on your car dashboard in the middle of a hot sunny day, or worse yet, in the middle of a cold winter. Batteries hate being charged at temperature extremes, especially below 60 °F (or 15 °C), and above 95 °F (or 35 °C).
  • If you are not traveling or need your phone fully charged all day, then charge your battery to about 80 or 85% — not to 100%. This will also help being gentle on the battery. 

More later.

18Sep 2014

The most common complaint about the battery is that it “does not last.” In other words, we have in our minds the expectation that our mobile device shall remain powered by this battery for an indefinite time…and when it’s empty, it should recharge very quickly. We will revisit these concepts and solutions to them in subsequent blogs, but for now, I want to set, or rather reset, a few expectations.

First, remember to charge your better whenever you can. An empty battery is useless, and waiting 2 or 3 hours to charge your battery is very inconvenient if not annoying. Yes, you can carry one of these battery sleeves, but now you are carrying a brick, not a thin and stylish smartphone. 

If you can and have the time, charge your mobile device using the USB cable attached to one of the ports of your PC or notebook. Yes, it is slow, but it will recharge the battery as you are working on something else. If you are at your desk, you don’t need the charging speed. And it’s way better than getting to your car and realizing you are now down to 20% remaining charge.

If you don’t sit at a desk, or you don’t have a notebook or a PC, put a couple of standard wall chargers around your house, and give your device some charging whenever you can. Of course, try to remember to charge your device at night. There’s no magic in this…it’s just some simple discipline to start with. 

For an Apple mobile device, you can use the Apple wall chargers in addition to the USB port on a PC or Mac. Don’t worry about using an iPad wall charger to charge an iPhone or vice-versa. An iPad wall charger will not charge an iPhone any faster (well, with the rumored exception of the iPhone 6 Plus). 

For an Android device, you can use a standard micro-USB wall charger (also known as AC adapter) as well as a USB port on your PC…it’s your choice. If you try to use a tablet AC adapter to charge your smartphone, there is a small risk you may damage your smartphone battery. That’s because if your smartphone is fairly new, say a year old or less, then the software inside your smartphone will protect it from drawing too much power and damaging its battery. But if you smartphone is older, then there is a risk it will draw more power from the larger tablet adapter and damage the battery.

One last tidbit…the difference between the wall charger of a tablet and a smartphone is the power rating, in other words, how much power the charger is capable of providing at its output. If you look at the standard AC adapter that comes with your smartphone (iPhone or Android or Windows), it will read typically “5V / 1.2A output“.  This means that it is capable of providing a maximum current of 1.2 Amps at 5 Volts, or an equivalent output power of 5 x 1.2 = 6 Watts. Output here is the electrical power that flows through the USB cable to your mobile device.  In comparison, a tablet AC adapter will provide nearly twice that power or about 12 Watts. 

Finally, a car charger is very similar to your standard AC adapter. The difference is that the AC adapter takes 120V from your wall outlet and converts it to 5V that your mobile device can use. The car charger, by comparison, takes 12V from your car cigarette lighter outlet, and converts it to 5V.

17Sep 2014

The lithium-ion rechargeable battery lives in many of our devices today, from our laptop PCs, to our tablets, and our smartphones, and many other devices that are not tethered to a power outlet. It has replaced the older generation of batteries such as nickel-metal-hydrides (also known with their abbreviation NiMH) and the more toxic nickel-cadmium (NiCd) batteries. You can still buy NiMH batteries at your local electronics store or Amazon: they are the size of the standard AA or AAA battery but can be recharged about a hundred times. They tend to be useful for your light torch or your children’s toys, but they are not used any longer in mobile devices or other gizmos that require longer battery life.

The lithium-ion battery is today’s king of the hill. It contains about 5 times more energy than the NiMH battery…in other words, it lasts 5 times longer. It comes in many different shapes; it can be a cylinder or it can be in a thin flat rectangular shape such as the one in your iPhone. It also requires proper care and operation. For example, if not properly charged in its appropriate wall charger, it may catch fire or worse yet, explode. 

lithium ion battery in iPhone 6
Lithium-ion battery in the iPhone 6

One of the key characteristics of a lithium-ion rechargeable battery is its maximum capacity to hold electrical charge. This is measured by the amount of electrical charge when fully charged, and is given in units of milliamp-hours, abbreviated as mAh. It is not a unit of energy. It is a unit of electrical charge. Higher numbers are better. More electrical charge means longer life and longer use time. Think of it as a bucket of water….capacity tells you the volume of your bucket. 

To convert from electrical charge to energy, one multiplies mAh by the battery voltage. Most lithium-ion batteries have a voltage of about 3.8 Volts (notice, this is way less than the typical 120 Volts out of your home outlet). So if we take the iPhone 6 battery, its capacity is 1,810 mAh (look at the bottom of the battery photo). When we multiply it by its voltage 3.82 Volts, then we get an energy of 6.91 Watt-hours (abbreviated as Wh). Once again, higher numbers are better.

So let me put this in perspective. One gallon of gasoline contains 34,000 (yes, thousand) Watt-hours. One gallon of gas has the equivalent energy of nearly 5,000 iPhone 6 batteries. So a takeaway here: You should appreciate why it has been difficult to make rechargeable batteries last for a very long long time.

Now, just because you have a bucket that has a given volume, it does not mean that you have that much volume of water in the bucket. First, you need to fill your bucket. That’s exactly what “charging” does to the battery. It fills it with electrical charge. When the battery is fully charged, its battery meter reads 100%. That’s the little gauge that shows up on the upper right hand side of your smartphone screen. Surprise, surprise, it is called the “fuel gauge.” When you use your battery, the meter reading decreases until it gets to 0%. Presumably, your anxiety level has risen a lot before you reach the zero level.

Ok, now here’s a little secret. Zero-percent reading of the fuel gauge is not really empty. It just means that you can no longer take charge out of the battery — mostly for safety reasons. The electronic systems in your device are smart enough to say STOP and shut it down. So it’s ok if you take your mobile battery to zero. It may be inconvenient to have an “empty” battery but it will not damage your lithium-ion battery. And no, there’s no memory effect in lithium-ion batteries.

More later.