We’ve all experienced that moment of panic when our smartphone, tablet, or laptop beeps and gives us that all too familiar five-percent of power remaining warning. Most of the time, this low power warning is nothing more than a reminder that we need to connect our device to a power source to recharge its battery. The issue of battery life vs power consumption of electronic devices has plagued engineers since before the transistor radio was first invented, and those challenges have remained the same even with modern leaps in battery technology.
To fully understand the issues with battery life, lets start back at the beginning of what I consider the birth of modern battery technology. In 1859 a French physicist by the name of Gaston Planté invented the lead-acid battery. While there were several battery designs previous to this, the lead-acid battery is still in use today in most parts of the world. While this design is able to store massive amounts of energy, the trade-off is size and weight. A small lead-acid battery might be able to power your smartphone for five days, but that battery would be several times the size of the phone and 20-30 times the weight. At the time of their inception, there were no “portable” electronics to speak of which meant that battery size and weight were not an issue.
Vintage lead acid battery
Fast forward about 100 years and the common alkaline battery was introduced. alkaline batteries while smaller and lighter, are very limited in the capacity of energy they can store due to their small size and zinc-carbon construction. However, these small batteries were just what the engineering world was waiting for. Thanks to fast paced developments in the semiconductor world at Bell Labs just a few years earlier, the transistor had been perfected enough that it was now being mass produced. This lead to the development of the transistor radio, and the birth of frustrations with battery life.
While it’s not considered the first portable electronic device, it is arguably the first portable electronic device that became a worldwide sensation. Previous “portable” radios needed several different batteries to heat up the tubes that powered them, and then to sustain the radios operation. The much smaller transistor radio utilized the then common flashlight battery (C cell) or the new 9-volt cells which were specifically designed to power these new radios. Depending on the volume at which these radios were operated at, the end user could expect anywhere from four to six hours of use from a single 9-volt battery.
Vintage alkaline batteries
Moving forward to the late 1980s, the invention of the nickel metal-hydride battery revolutionized the way consumer electronics were produced. The new NiMh batteries featured a higher energy storage capacity than their alkaline predecessors. The biggest advancement though was the ability to safely recharge these batteries in a household environment, and not have to worry about hydrogen off-gassing. A typical AA-sized alkaline battery boast an average of about 750mAh, while a NiMH AA cells usually pack in about two to three times the capacity.
Current state of the art battery technology lies in one of the most volatile metals on the planet, lithium. Research and experimentation into using lithium in batteries has been taking place since 1912 and has made quite a few advancements over the last two decades. The first commercially available lithium-based batteries were created in the 1970 for industrial and scientific use. The modern lithium-ion battery made its first public appearance in 1991, and was manufactured by Sony. While the lithium-ion battery still exist, and is used in everything from electric vehicles, space vehicles, and electronic cigarettes, its successor, the lithium-ion polymer battery is far more common. By infusing the lithium metal in a solid polymer composite, the battery’s shape can be molded into flexible packs, which makes it perfect for the mobile device market. If you have a modern cellphone, smartphone, tablet, laptop, or other rechargeable portable device, it is almost certain to have a lithium-polymer battery at its core.
An Assortment of Modern Batteries featuring a lithium-polymer cell on the left and a NiMh cell on the right.
While alkaline, and nickel-based AAA-D sized cells have a nominal voltage of about 1.5V. Modern lithium-ion batteries are built into 3.6v cells that can be combined to create 7.2, 11.1, 16.8V and so forth. A typical 18650-sized lithium-ion battery will have a capacity of somewhere between 2000mAh and 2500mAh. To get the same voltage and capacity you would need at least 4 alkaline AA batteries, making lithium-ion the clear choice for modern portable electronic devices.
Pre-Moores Law to 2025
So with the huge leap from lead acid batteries to lithium-ion cells, why are we still complaining about battery life? It’s quite simple actually, and we just have to look to a man named Gordon Moore, the co-founder of Intel. In 1965, Moore made an observation that the number of transistors per square inch had doubled every year since the invention of the integrated circuit in 1958 by Jack Kilby of Texas Instruments. In 1975, Moore revised his “law” stating that the number of transistors would double every two years for the foreseeable future. It’s been 50 years since Moore first made his original observation, and it has held true ever since.
The first Integrated Circuit next to a modern PC CPU with billions of transistors
The first integrated circuit featured two transistors, but modern ICs such as Intel’s Xeon line of computer processors can feature over 4-billion transistors in a single chip. This exponential growth of transistors is the reason that we complained about battery life in the 1950’s and still continue to struggle with finding a proper balance between power consumption and battery capacity today. The fact that a small , , or smartwatch on your wrist has more processing power than the Lunar Lander and LEM modules that went to the moon in 1969 combined is an amazing feat within itself, but when you come to realize that modern battery technology can still provide us with an all day radio stream despite its much slower development progress is a little mind blowing.
What does all of this mean for engineers? To me it means that when designing a project, I have to be more conscious of how much power the devices I design actually consume. With the advancement of low-power sleep modes on many modern processors, it is quite easy to design simple products that barely sip energy. While the practice is commonplace in the professional engineering world, many of us who do not design products on a regular basis often take shortcuts, when designing the electronics for our projects. This is often in the form of using a fully featured development board to handle simple task such as addressing the of , powering a , or even tracking things like environmental metrics such as .
Digital Clock Built with a Raspberry Pi. Image Courtesy Adafruit.com
While using a to report the temperature of your office to your smartphone every 30-minutes is a pretty cool project, it's simply a waste of energy. Something similar could be done with an and a small module that is only woken up every half and hour to record and report the metrics to your phone.I have seen a lot of clock projects from engineering students and hobbyist over the years that utilize an and a to accurately keep time, but these projects usually devour a 2000mAh in about a day or two. That is horrible efficiency for something as simple as a clock. By utilizing an MCU with a super low power sleep mode and you could easily extend that watch’s battery life to days or even months.
Those may be bad examples when looking at things from a professional engineers standpoint, but the point I am trying to make is that unless you need all of the bells and whistles that something like an has, you should consider a much smaller, and less featured MCU when designing with power consumption in mind.
As a tech writer for the better half of the last decade, I have been following the advancements in mobile devices and now the wearables industry, and I am seeing a lot of concessions being made in the name of longer battery life, but I also continue to see blatant battery hogs being created with no thought whatsoever being given to energy consumption. I will admit that manufacturers of mobile technology have made leaps and bounds in this regard though. My first smartphone back in 2008 had a battery life of about 4 hours with less than 30 percent of the features that my current LG G4 has which on average last about 36 hours on a single charge and moderate use.
What you are willing to give up on projects in an effort to drop a few milliamps of power consumption? And what you will not compromise on no matter how much energy that feature draws? I would love to hear about where you think battery technology is headed, and when we might (if ever) see the curve of transistors per inch and battery efficiency once again cross paths.