Solving the smartphone battery problem: Idle Charging

Let's take a moment to review our day-to-day experiences with batteries, charging, and our beloved smartphones.

Most of us charge our phones overnight to be ready for battle the next day. Some of us carry heavy, expensive, and frankly, inconvenient, battery packs with us to keep our boats afloat throughout the day. And even for some of us with the latest smartphones with the biggest batteries, we end up charging our devices by the evening when the battery level starts hitting below 40%. That's not uncommon! In fact, a 2016 survey by LG reported that 9 out of 10 people suffer from "low-battery anxiety" [1]!

Smartphones play such an important role in our lives these days that our daily life halts whenever our phones die. So how do we improve the battery life? Well, we can jam in a bigger battery in our phones or invent a denser battery technology, but these solutions are easier said than done. So a few months ago, when I shot down a zombie in Call of Duty with my rechargeable laser gun (with infinite ammo!), I had an epiphany: "Wouldn't it be cool if my phone had infinite 'ammo'? It should just recharge whenever I'm not using it! Heck, I don't really use my phone most of the time."

When I investigated further I found out that, on average, smartphones are kept idle 89% of the time [2]! However, even when idle, smartphones typically have background processes running all the time that consume almost half of the entire battery life. So what can be done?

I began wondering, "What is the most ubiquitous form of energy that can be harnessed wherever my phone is all the time?" The simple answer was "Light"! Wherever we are, in our homes, offices, parks, etc., there is light. Just as our lives halt without smartphones, so they do without light. So if we can harvest enough energy from the ambient light while our phones are idle, we might be able to emulate the experience of "infinite ammo" with our beloved smartphones. As a result, I dubbed the process of charging a device at a rate greater than or equal to the rate of power consumption of the device when it is idle as idle charging. This thought paved way for the bigger (admittingly somewhat quixotic) vision:

Imagine putting your phone down on your desk at 53% battery level. You then check your phone after 3 hours and are shocked to see that your battery level has only risen to 55%.

We are so used to complaining that our phone battery went down by so much. Imagine the entire experience reversed: we will instead start complaining that our phone battery went up by only so much. Picture finally opening up your laptop after a few days and finding it fully charged. Or your smartwatch or wireless headphones (or the numerous IoT devices that you will soon have) that have been lying on your side-table for days and when you finally need them, they are automagically fully charged.

Now that I've gotten you excited about this vision, allow me to also put our feet on the ground. Through my research, I discovered, there is not enough ambient light around us, i.e. in our houses or offices, that can make this dream of infinite battery life for phones a reality because smartphones consume a lot of power (1-2 Watts) during active use. However, turns out that there is enough ambient light available to extensively prolong the battery life.

"Solar Energy Harvesting" specializes in converting ambient light into electricity with high efficiency. As you'd expect, it consists of a solar cell and a bunch of electronics to maximize the efficiency of energy production. You might be thinking that there are a ton of solar phone chargers already available on the market. But during my research, I found out that conventional solar chargers drastically fail indoors [3]. And adding to the misery, according to a comprehensive survey done by Environmental Protection Agency, people in the U.S. spend more than 92% of their time in enclosed buildings [4]. So if we want to design something that works all the time, wherever we are, we need a technology that works well both indoors and outdoors. Point to be noted: our design won't work when the phones are in our pockets and during night time since they will not be exposed to ambient light for energy harvesting.

A ray of hope was shown by the exemplary work of some researchers who have successfully manufactured solar cells with novel materials such as Gallium Arsenide (GaAs), Dye Sensitized (DSSC), and Perovskite. These cells not only boast unprecedented efficiencies in indoor lighting but are also already in production by companies such as Alta Devices, GCell, and Saule Technologies respectively.

When I combined the model of how people behave with their smartphones with the indoor and outdoor light conversion efficiencies of these new materials, I came up with a state-of-the-art design that could get us an inch closer to idle charging. With a solar cell the size of an average smartphone and based off of these new efficient materials, we can design a system which can extract up to 4-15 mW of power indoors. Moreover, the latest phones only consume about 30 mW of power when they are idle [5].

So, if my math is correct, we can potentially double the amount of standby time of the phone! And since almost 90% of the time our phones are in this standby mode, I'm now talking about making the entire user experience with smartphone battery-life twice as better! And the full system is not heavy or expensive like the rechargeable battery packs, but ultra-thin, ultra-lightweight, and relatively inexpensive. It is the most unintrusive way of inconspicuously increasing the battery life of your devices.

I can already envision ordinary looking phones cases that offer battery life extension or thin transparent screen guards that have photovoltaic capability. The goal of spreading the concept of idle charging is to see how this technology flourishes in the hands of the innovative minds of the world. If you are interested in reading the technical details regarding this research, feel free to shoot me a message. My theoretical paper on idle charging titled "Energy Harvesting for Idly Charging Smartphones to Improve Perceived Battery Life" is to be published in the Proceedings of IEEE Intercon 2017 and could also be accessed through IEEE Xplore library starting mid-August, 2017. I am currently developing a prototype and will report the performance analysis in future publications. So stay tuned!

Let me know what you think about the ideas presented here and/or if you are interested in learning more about how this technology can be applied to your business.

References

[1] “Low Battery Anxiety Grips 9 Out Of Ten People,” 2016. [Online]. Available: https://www.prnewswire.com/news-releases/lowbattery-anxiety-grips-9-out-of-ten-people-300271604.html.

[2] A. Shye, B. Scholbrock, G. Memik, and P. a. Dinda, “Characterizing and modeling user activity on smartphones,” ACM SIGMETRICS Performance Evaluation Review, 2010.

[3] C. Li, W. Jia, Q. Tao, and M. Sun, “Solar cell phone charger performance in indoor environment,” in 2011 IEEE 37th Annual Northeast Bioengineering Conference, NEBEC 2011, 2011.

[4] N. E. Klepeis, W. C. Nelson, W. R. Ott, J. P. Robinson, A. M. Tsang, P. Switzer, J. V. Behar, S. C. Hern, and W. H. Engelmann, “The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants,” Journal of Exposure Analysis and Environmental Epidemiology, 2001.

[5] D. Ferreira, C. Schuss, C. Luo, J. Goncalves, V. Kostakos, and T. Rahkonen, “Indoor light scavenging on smartphones,” in Proceedings of the 15th International Conference on Mobile and Ubiquitous Multimedia MUM ’16. New York, New York, USA: ACM Press, 2016, pp. 369– 37.

Picture credits: LG Electronics and live-smart.co

Editing credits: Vishrut Poddar