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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.

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16Sep 2014

1. JUST A SIMPLE INTRODUCTION.

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.

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