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June 30, 2015


Electronics & Systems
Fast Charging
Nadim Maluf

That is 3,000 mAh….this is the battery capacity that consumers will see in most mid-tier to high-end mobile smartphones for the foreseeable future. Why? It’s simple, this is the capacity that gives consumers an honest full day of operation.

This begs a first question: what is an honest full day? no one really knows since usage varies considerably across the consumer base. But manufacturers are not able to tailor the battery to different consumer groups, therefore, an honest full day of operation ought to fulfill the demands of the largest cross section of consumers, including the spectrum from travelers to stay-home parents and teenagers who are glued to their favorite social network app. It would be fair to say that an honest full day ought to deliver at least 10 hours of talk time per day, preferably more, and at least 10 hours of screen usage time, including web browsing and app usage.

The two charts below examine talk time and web browsing time for a number of commonly available smartphones as measured by GSM Arena in their battery tests. For talk time, the relationship is immediately obvious. More battery capacity equals more talk time. Simple and easy.  Some smartphone makers are a little better than others, but overall, there is a simple relationship that says that about 3,000 mAh gives about 20 hours of 3G talk time. Now these are lab-based tests, so in real life, you would want to give yourself a little extra margin.  But I would say that 3,000 mAh is probably sufficient for most phone-talking needs, most likely lasting you several days if all you do is only using your smartphone to talk.

Now, talking on the phone does not need the screen to be turned on, but everything else, from simple messaging to browsing and app usage does. The screen is a major power hog as I explained in a previous blog. This is where the battery begins to get challenged. The next chart shows measured usage time for web browsing, a good proxy for having the display as well as the radios turned on.

The picture now gets a little more involved. Clearly a bigger battery equals more time, but also the choice of smartphone does matter. For example, Apple and Sony seem to do a better job managing the power budget than HTC and LG do. Nonetheless, the chart is also specific in saying that if you are gunning for about 10 hours or more of screen time per day on a device that has a 5-in display, then the battery capacity needs to be right around 3,000 mAh (or more).

So there you have it….anything less than 3,000 mAh will leave consumers unhappy with their battery performance. Anything much more than 3,000 mAh will leave the manufacturer with a more expensive battery that will not likely earn this manufacturer any additional sales. So it seems that 3,000 mAh will be the right figure for a little while.

Now let’s find the approximate charge times for such a battery. Such a battery has an equivalent energy of about 11.5 Wh. So a standard 5-Watt AC adapter will charge this battery at nearly 0.4C (=5/11.5) for which the charge time is an agonizing 3+ hours (see my earlier post on charge times). New AC adapters capable of charging at 12-18 Watts will accelerate the charge times. In other words,  such larger batteries will undoubtedly go hand-in-hand with fast charging…and that’s what consumers will want to see in their mobile smartphones soon: a full-day battery that can be charge in the fastest possible time. Expect such new crops of smartphones to emerge in 2016.

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