A look inside the world of batteries

19Sep 2014

Yes, I did. That’s when you wake up a few months after you make a proud investment in a new mobile device, then you realize that the battery is not lasting as long as you wanted.

Well, first to be safe, you have to make sure that you don’t have too many apps running in the background draining the battery without your knowledge or your permission. But assuming that you already reset your phone, deleted the useless applications, and turned off all the background app refreshing, and you are still not getting the battery life that you had only a few weeks or months ago, then you are right, you are now experiencing the signs of battery damage, or in geek terms, it’s called “capacity fade.”

Remember when we talked earlier about the charge capacity of a battery and said it is measured in units of mAh. So let’s say that you battery is rated at 2,500 mAh. So when your device is fully charged, and your fuel gauge in the upper right hand corner of your screen is reading 100%, it means that your battery is holding about 2,500 mAh of electrical charge…using the earlier analogy of the water bucket, it means the bucket is full and is holding some number of gallons of water.

But this assumes that the battery is new. As damage sets in the battery, its maximum capacity will actually degrade over time and use. This can happen for many reasons, such as poor manufacturing, extended exposure to low or high temperatures…etc. (we will get back to this at a later time). So the battery you have now has a maximum capacity of say 2,200 mAh instead of 2,500 mAh. In other words, you will notice a decrease in your battery life by about 1 to 2 hours per day.  

So now you are frowning, and possibly complaining: “But, but, but….the fuel gauge is still reading 100% when it is full.” Yes, the fuel gauge only reads the available charge in the battery as a fraction of the maximum available capacity in the battery (it’s a mouthful). In other words, on day one, your battery was able of holding 2,500 mAh, so 100% of the fuel gauge is then equal to 2,500 mAh. But after 6 months of use, the battery can only hold 2,200 mAh, and the 100% displayed by the fuel gauge is now equal to only 2,200 mAh. Ouch! 

If you are thinking about where you can read the lower battery capacity of 2,200 mAh, the answer is nowhere. You can’t. The smartphone manufacturer and battery vendors either can’t tell you or don’t want to tell you. This is called “state of health” of the battery. 

When the battery capacity drops to 80% of its original capacity — in our example here, it is 80% x 2,500 mAh = 2,000 mAh — the battery is deemed dead and must be replaced. But as you gathered, it has been difficult if not nearly impossible for customers and consumers to prove that they have a dead battery. 

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.

16Sep 2014


If you are a consumer who has wondered why your lithium-ion battery in your mobile device fails your expectations, this blog is for you. If you are technically savvy but you are not a chemist, and often wondered how this lithium-ion battery works the way it does, then this blog is for you. If you are just curious about how to get more out of your lithium-ion battery, then again, this blog is for you.

You have searched the internet for information on the battery inside your gizmo, how it works, how you should take care of it, what the fancy technical terms really mean, and what the manufacturer is promising you and what you are really obtaining….and I am sure you often felt frustrated because, well, little of it made sense to you. You are not alone.

The fact is batteries have for a long time been a forgotten corner of technology. Before mobile devices became anchored in our daily lives, the battery meant that blackbox under the hood of our cars. Batteries did not evoke “clean” or “high-tech.” We wanted a low-cost battery that cranked our engines even in the coldest days of winter.

Then came mobile devices, and now electrified vehicles… and things got more complicated. Everyone had an opinion, or a theory. “No, don’t discharge to empty!” or “Beware, it has a memory effect.” The fact is most of this advice is not based on real science and has little merits. True battery experts are hard to find…universities don’t graduate enough of them, and they are in high demand.

This blog is intended to be read either as individually independent posts, or collectively as one continuous reading. The titles are summarized in the Table of Contents on the right hand side. Start with whichever topic you would like depending on your fluency level.

In the next post, we will start with the basics: What the terms really mean when one describes a battery.