The first wirelessly rechargeable AA battery
Homo sapiens always felt that mastering fire is not enough; the dream was to tame the lightning. ⚡
We all experienced those warm summer nights: the rain hasn’t started yet, but we feel how unusually lull and calm it becomes. Suddenly, the lightning strikes the night sky like a razor splitting the heavens. Ozone scent hits your nose; the birds and nature are not audible anymore. You start counting the seconds until the rumble oscillates your eardrums, dividing the final sum in between lightning and thunder by magical number five, thereby calculating how many miles separate you from the approaching storm. Repeat it a couple of times, and now you know precisely how soon you’ll get wet. And the only rule of this game is that the speed of sound in air is 0.213 miles per second.
That feels amazing when you are outside; and when you are cozy inside?
The one law that never fails me and is as reliable as General relativity of Einstein is Murphy’s Law. When on any given rainy, windy day you decide to chill at home, you pick up the remote or a game controller; turn on the cracking sound of your artificial fireplace or romantic lights in your bedroom; get back to your DIY project or play with a remote-controlled drone; pick some notes on a synthesizer or electro guitar, and guess what — your batteries drop dead, as if they’ve been waiting for this particular moment! And those extra batteries you providently had just in case ran out of juice because of some mysterious and inexplicable parasite current.
Rechargeable batteries? Somehow you failed to adopt those, as you were consistently losing the branded batteries or displacing the proprietary chargers. So you come to an agreement with yourself to change your comfy pajamas for a sweater and raincoat and march straight to the corner store to get some Alkalines. And now you’re wet, half an hour short, and your initial chill mood has vaporized. That’s exactly when the ideas are being born, right? :)
This video is from May 2020, it’s me presenting you the first wirelessly rechargeable AA battery that can recharge from any Qi wireless charger.
Further reading is a long read, so for your convenience, I’ve added a table of contents (: if you are familiar with a subject, you can scroll to the topic of your interest.
Table of Contents:
- A historical bite in origins of the discipline
A brief history of Electricity, Transformers, and Batteries
- The birth of the first wirelessly rechargeable AA battery
The ultimate convergence or a glimpse into the wire-free future
- Prototyping: getting to know the basics
Wireless power or another useful derivative of the transformer
- Material fatigue and other fast-charge adventures
Battery conditioning and operation
- Prototyping: bringing to life
Wirelessly rechargeable battery creation, iteration, and accomplishments
A historical bite in origins of the discipline
What fascinates me most is that there is evidence of battery usage in ancient civilizations —just imagine, our predecessors used to make batteries two thousand years ago. Even more, whatever culture you belong to, most likely your ancestors worshiped a God of Thunder, sitting next to the bonfire or performing a tribal dance. And it doesn’t really matter where the balance between speculation and the truth stands. Understanding and domesticating electricity was a long time dream of humanity.
What was the most fascinating for many scientists is the relationship between electricity and magnetism. In 1820, the Danish scientist Hans Christian Ørsted carried out an experiment for which he is credited with the discovery of electromagnetism. He observed, that when he ran an electric current through a wire, a nearby compass needle was temporarily deflected from its stable position of pointing towards the magnetic north. A couple of months after Ørsted’s discovery, the French physicist and mathematician Andre-Maria Ampere had shown that two current-carrying wires placed in parallel close to each other generated magnetic lines of force that caused the wires to be attracted or repelled from each other depending on where the currents were flowing in the same or in opposite directions. Another French physicist by the name of François Arago carried out an experiment that completely baffled most scientists: in 1824, he demonstrated that a spinning copper disc caused a magnetic needle suspended above it to rotate. This served as one of the main motivations for another brilliant physicist, Michael Faraday.
In 1831, Faraday found out that when the permanent magnet is moved in and out of the round copper coil — the electrical current is induced. That led him to the discovery of electromagnetic induction. I like to imagine all those geniuses locked in a room, describing through a set of precise experiments tail, trunk, and feet —and then, one of them shouts out: “Look, it’s an elephant!”. I think of James Clerk Maxwell as the one who managed to see the elephant. Maxwell’s development of his theory of classical electromagnetism in 1865 led directly to the development of the electric dynamo and electric motor, two technological advances that are the very foundations of the modern world. Describing the big picture enabled even more scientists and engineers to start the experimentation with the electromagnetic phenomenon, as now they had Gauss’s, Ampère‘s and Faraday’s laws available to them in the beautiful and logical equation union. It took around 30 years to understand and tame the alternating current since all the experiments were built around the direct current at that time.
“The heart of the alternating current system” William Stanley Jr.
Once humanity got ahold of alternating current, the next question was — how to control it?
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors — the transformer’s coils. It is a crucial part of the web of wires and poles that distributes energy and deliver power to all countries around the globe. Transformers are used to bring the voltage up or down, convert the AC and DC power in multiple ways, send and receive the radio signal and so much more. It is essential for powering the cities, electric cars, consumer electronics, or just a tiny circuit of your handheld watch.
From the 1870th to 1890th there was a tremendous leap in transformer design research and optimization. In 1884 the productive union of Ottó Bláthy, Miksa Déri, Károly Zipernowsky of the Austro-Hungarian Empire led to the first designed and used transformer in both experimental and commercial systems, improving the Gaularad’s transformer that made a 25-mile long transmission illuminating arc lights, incandescent lights, and a railway. George Westinghouse and William Stanley made the first transformer with a core of E-shaped plates which was practical to produce and stays popular to this day. A bit later, Albert Schmid improved the E-shaped plates extending them to meet a central projection. In 1889 Mikhail Dolivo-Dobrovolsky developed the first three-phase transformer in Germany at AEG. And that is a known 3-phase technology that we have been using to this day. When finally, it’s not important if it is a transformer, motor, or a generator — they all have the same underlying principle:
Electricity creates magnetism and vice-versa.
But all those electrodynamic discoveries would not happen without a power source. While scientists were struggling with dynamo machines, barbarously choking the gorgeous sinusoid of the alternating current and still yet to figure out the necessity of iron in the construction — the batteries were the best way around to conduct the measured experiments. And that brings us back to the battery story.
The battery converts chemical energy into electrical one.
American scientist and inventor Benjamin Franklin first used the term “battery” in 1749 in his experiments with electricity, for which he used a set of linked capacitors. In 1796, an Italian scientist Allesandro Volta noticed that the voltage potential of dissimilar metals became the stronger the farther apart the affinity numbers moved. The first number in the metals listed below demonstrates the affinity to attract electrons; the second is the oxidation state:
Zinc = 1.6 / -0.76 V
Lead = 1.9 / -0.13 V
Tin = 1.8 / -1.07 V
Iron = 1.8 / -0.04 V
Copper = 1.9 / 0.159 V
Silver = 1.9 / 1.98 V
Gold = 2.4 / 1.83 V
Carbon = 2.5 / 0.13 V
He thus understood that certain fluids would generate a continuous flow of electrical power when used as a conductor. This discovery led straight to the invention of the “voltaic pile” that would lead to the electrical revolution. Volta’s invention quickly captured the attention of the world, so the battery improvement race has begun. The Grenet Cell “The Bottle Battery” was invented in 1857 and lasted for over 60 years, proving to be a very powerful and reliable wet cell. Parallelly, Gaston Plante of France invented the Lead Acid Battery in 1859 — the first rechargeable battery. In 1886, Karl Gassner developed dry cells; it was a huge improvement for some applications of the battery. In 1899, Waldemar Jungner from Sweden invented the nickel-cadmium (NiCd) battery that used nickel as the positive electrode and cadmium as the negative. Two years later, Thomas Edison replaced cadmium with iron, and this battery was called nickel-iron (NiFe).
In 1991, Sony commercialized the lithium-based batteries. You most definitely have heard of them as they are powering your portable electronics, such as laptops, phones, cameras, power tools, medical devices, and electrical vehicles from bicycles to satellites. The lithium-based system proved to have high energy, simple charging, low maintenance, and less harmful to the environment.
The birth of the first wirelessly rechargeable AA battery
..So here I am, standing at the corner store.
It is raining, half wet and half frustrated choosing between two well-known brands and being baffled at both of them hiding the ampere-hours and watt-hours that the battery contains, as if this was a trade secret. The confusion piles up after each crusade for a new pack of Alkaline batteries and makes me think: it is the 21st century.
Why are we are still wired to the century-old technology when we are clearly living in the wireless world? We’ve produced hundreds of billions of consumer devices powered by batteries over the last decades, and we still sell billions of batteries each year and dispose hundreds of tons of those into our landfills. One of the first consumer devices operated on battery power was patented in 1899 (flashlight powered by multiple ‘D’ batteries) by David Misell and later acquired by Eveready Battery Company. Even though over the last decade we’ve been actively switching some of our electronics to the slim li-ion batteries with separate multi-standard USB charging systems, the battery-operated devices are still all around us. Remotes of many kinds. VR and game controllers. Lights and camping gear. DIY and remote-controlled projects. Toys and music instruments. Oxygen meters and Holter monitors.
We live in a time when every smartphone has a wireless power receiver; cars and furniture manufacturers make the wireless power transmitters factory embedded and that’s only the beginning of the list. All the software updates and communications are successfully done over the air through the radio channels. The paradigm of the tangled and broken cables of many standards is emerging into the new inductively coupled world and brings us one step closer to the resonant future.
What a beautiful concept of replacing all the bulky wires, abandoning inconvenient USB formats with proprietary chargers, and always finding your recharged device at the same spot or being able to recharge practically anywhere.
My curiosity in electrodynamics came very handy. Given that Wireless Power Consortium has been promoting the adoption of Qi technology for the last 12 years and now the wireless charging popularity is rising to the moon, it means that in a couple of years every household, public place, and the personal vehicle will have a wireless charger available. That made me think:
What if the conventional battery could be reinvented?
Goal — ultimate convergence
- Create the first wirelessly rechargeable AA battery
- Charge it from any Qi wireless power transmitter
- Recharge with or without extraction from the device 🤞
- Build something convenient and competitive while helping to improve the environment
- Make it last.
Prototyping: getting to know the basics
Over the last decade, we’ve seen the rise and fall of many wireless charging standards. Some of them got focused on being exclusive for specific industries, while others focused on broad adoption through the biggest consumer brands. My standard of choice became obvious: the one that Wireless Power Consortium has been advertising for quite some time. You know it as a Qi wireless standard. Any Qi wireless power transmitter has at least 5 Volt and 1 Ampere or 5 Watts written on the box. Some companies produce more complex systems with a set of multiple coils and more sophisticated power management to deliver additional energy over the larger surface. All wireless technology is a derivative from the transformer, another useful application of the crucial invention. Why now? The wireless charging market has grown 4X times since 2016 and has an exponential tendency for the expansion rate. We have a rapidly growing market full of unified wireless power transmitters waiting to be resonantly coupled with any supporting receiver, and billions of battery-powered consumer electronics.
Texas Instruments, Freescale Semiconductor, Integrated Device Technology, and many other companies designed and produced the wireless power transmitter and receiver controllers that significantly simplify the given task. After a couple of years spent tinkering with ECG signals on ADS1293, Texas Instruments became the choice for many electronic components; the wireless power receiver wasn’t an exception. The BQ51013B wireless receiver became the perfect fit for 0.53 inches PCB disc. Let me give you some simplified details from under the hood of the Qi standard and wireless power transfer that makes all the magic happen.
The basics of the wireless power transmitter are the following: we need to bring our transformer coil with a ferrite plate below to the saturation point, a hundred thousand times per second at least, to reach the frequency defined by the standard. Having a DC current, oscillated controller or multivibrator, gate driver, two transistors with high and low current limit comparators, a handful of capacitors and resistors — is all it takes to create a basic electromagnetic field with an AC current of the preferred frequency. This procedure creates a meander also known as a square wave in the primary coil of the transformer.
The full picture is a bit more different. We have a ping and communication layer at the speed of 2kb/s to avoid unnecessary energy waste. Foreign object detection prevents your wireless power transmitter acting as an induction oven :) And some more..
For the wireless power receiver, we have another part of the transformer that has a coil with a ferrite thin sheet above, a secondary coil. First, we need to set the receiving coil to the resonance state: knowing the impedance and inductance of the coils with an included core, we can calculate which capacitor to add. Or, simply playing around with capacitors and an oscilloscope, we can find the one that will get us to the resonance state. How resonance works: imagine that you push a swing, with both hands — there is the amount of energy you need to apply to make it swing until you reach equilibrium to keep it at the same pace with a point of your finger.
The synchronous rectifier converts the AC current to DC, making it suitable for charging purposes. And that is another significant benefit of BQ51013B: you don’t need to implement the separate Shottky bridge rectifier while losing power on the voltage drop or expand your circuitry form factor by LT4320. Then the charge controller brings the power to the necessary charging point and sends it straight to the rechargeable battery cell. That happens many thousands of times per second, like an ocean wave countlessly hitting the shore.
Once the frequency of the primary and secondary coil is in the resonance, the resonant contours are in the needed proximity and the communication message to activate the transfer has been sent — then the power transfer efficiency reaches the maximum mark, without counting the electrons that are being dissipated through the air, chosen material resistance and a rectifying bridge. The intensity of the passing energy is controlled at the wireless power transmitter by the frequency diversion, therefore, drawing coils away from the resonance.
And a tiny bit of info about the communication message, as I find it as a quite elegant solution for this particular purpose. The communication message lets the transformer know when to stop the ping and start the energy transfer. If there is a foreign object, a battery problem, circuitry logic fail, short circuit or overheating risk — the command will stop the transformer operation to prevent any kind of hazard. But there is no communication happening as we know it, it’s more like the transmitter is watching its own signal, and the receiver makes a little bite out of it to let the transmitter know the receiver’s intentions.
These are all the necessary steps to make the secondary cell charged, what’s next? Step down transformer brings the 3.7V Li-ion to the necessary AA output, creating a stable 1.5V output through the entire battery life without any power disruption. Thanks to the circuit logic, the voltage of the secondary cell will never fall lower than 2.5V so we can safely state that it cannot physically drop below the 1.5V. The set of diodes, resistors, transistors, and thermistors — protect the power source from the short circuits, reverse polarity, overcharge, over-discharge and thermal impact.
She‘s Alive! She’s Alive! But for how long?
Material fatigue and other fast-charge adventures
In 1870, the Wöhler introduced the Wöhler curve, also known as Fatigue Curve or SN-curve. It is a plot of the magnitude of alternating stress versus the number of cycles to failure for a given material. The most popular rechargeable batteries in consumer electronics are Li-ion based batteries, with chemical compounds of all kinds, such as Lithium Cobalt Oxide, Lithium Manganese Oxide, Lithium Nickel Manganese Cobalt Oxide, Lithium Iron Phosphate, Lithium Nickel Cobalt Aluminum Oxide, Lithium Titanate, etc. Each of those materials, when used together, produces specific battery operating conditions. Why so many? It’s the latest 30-years race on who will create a better material mix that will hold the most capacity with a little to no self-discharge, improve charge and discharge rates, oh, and no explosions or fire, please.
I like to think of Fatigue Curve as a metal spring that you hold with both hands with an irresistible temptation to expand and contract it, like playing the accordion. Now, imagine that you are strong enough to expand the spring to horizontally outstretched arms and then contract it, almost collapsing the poor thing. What will it do? It will create an enormous amount of stress on the spring and initially make it stretch and most likely break. But as any metal spring, it is originally designed to expand and contract, you just need to operate in the spec of the given spring to maximize the life cycles of one.
The battery follows the Fatigue Curve model for a metal spring, it is just the variables for expansion and contraction are different in the electrochemical application.
SoC or State of Charge with Charge Rate — responsible for expansion.
DoD or Depth of Discharge with Discharge Rate — manages the contraction.
It’s always a trade-off, as all these variables tap directly into the battery capacity and operation. The ultimate equation of how to increase the charge cycles and improve the lifecycle of the consumer electronic device while decreasing the capacity sacrifice of the given battery and not to overload the chemical compounds with unnecessary stress. The rechargeable batteries should not lose the 30% of available capacity by the 1000’s recharge cycle when they managed properly.
Another bright mind of the electrodynamics is Coulomb — not the Genoa’s one who sailed across the ocean and is remembered for introducing all the world to the tobacco smoking discipline, but rather a French physicist, Charles Augustin de Coulomb, the inventor of the C-Rate that derived from the Law named after him. What is C-Rate and why is it important? Charge and Discharge rates of a battery are governed by C-Rates. 1C Charge Rate means that the battery of any capacity will charge in one hour if the power source will allow. Therefore 0.5C or C/2 means that it will recharge in two hours when 2C gives recharge in half an hour. The Discharge Rate is exactly the same but in reverse.
Let’s say that an average smartphone li-ion battery is 3.7V 3,000mAh or worth of 11 watt-hours. A conventional charger has an output between 5 to 10 watts. The fast charge claims 15 watts of power delivery. Let’s review the 10 watts or 5V 2A charger first: the charger output allows us to recharge the smartphone battery in 1.5 hours if we apply a 1C charge rate. In case of fast charge, 50% of charge in 30 minutes means that we need to send 1500mAh or apply a continuous charge rate of 1C for half an hour to fill 50% of the battery.
Normally it would take us three or more hours to charge the phone from the conventional charger. Longer charging doesn’t mean outdated technology or approach — the li-ion battery with defined chemistry has its own limits in the charging C rate that you can safely apply without creating the material fatigue of the chemical compound. That’s why the fast charge approach is very questionable even if it takes only a half an hour and then drops the C rate to an acceptable norm. As a result, it makes your electronic device power source significantly degrade in a matter of one to two years, therefor shortening the battery life expectancy and finally your user experience.
“Batteries are the most dramatic object. Other things stop working or they break, But Batteries… They Die.” Demetri Martin
With all that in mind, I concluded that different battery chemical compounds will bring various benefits, depending on the operation and application of the power source.
In the current prototype, the main focus is to bring as much capacity as it’s physically possible to fit inside of the AA case while finding the balance between charge rate and battery life longevity.
The same principle is applied to the discharge rate, but I’ll take this topic to a separate article on the fast charge and discharge capabilities without sacrificing the battery life longevity.
Prototyping: bringing to life
As one said: “Vision without execution is hallucination.” Let's get started!
The decision was made to start with an AA battery replacement, as it possesses the biggest market share and is big enough to fit the circuitry logic without exceeding the original form factor, and 3d-printed an AA battery case that would comprise the rechargeable system. After forming self-made antennas, I started experiments with wireless power in order to figure out the resonant contour capabilities.
The promising concept proved to be a fully working model. The receiver worked as designed, the power cell was charging following our Fatigue Curve formula. The PCB board was able to fit all the necessary safety features as Overcharge, Reverse Polarity, Short Circuit, Over-Discharge, and Thermal Protection. No voltage degradation was present, the battery had a constant voltage of 1.5V till the last breath. How would you place the round battery at the horizontal wireless charging pad without making it roll away? You cut the bottom, making it flat — very informative for the operator which side needs to be inductively-coupled. And even more, add a couple of tiny rare earth magnets and now you can place it with your eyes closed.
A calm night sleep without inductive nightmares returned to me. But not for long.. as the ‘What if’ started painfully rising in my head again, finally taking over the sleeping hours and putting us back to the prototyping bench.
While the mechanism was very elegant, you could open the case, insert another power cell into the battery cradle similar to Plug’n’Play, and recharge the unit on any wireless charger. But eventually, this ended up being the main constraint of the prototype, a massive case, and the cradle would eat all the AA space slashing hard the capacity of the system. That thought bothered me for a couple of months. The system comprising so many parts would complicate the production and unnecessarily increase the price of a single unit.
The clouds parted and the lightning hit me in the head, another ‘What if’ emerged, the team rolled their sleeves and so the new iteration began.
What if we get rid of all the parts, replace the flat circuit board with a round one in which we’ll fit all the electronic components without sacrificing even a tiny bit of safety or functionality, at the same time improving the capacity 2.5X times? Plus, the self-made antenna will be replaced by a flat ellipsoid. Sounds extreme? But you know what, Bingo!
And now I’m honored to introduce you to Her Majesty, Airiona Radiance.
5 minutes of charge gives you 95mAh at current 0.5C
A mouse consumes 25mAh or so and will work up to 4 hours.
A passive remote controller will last you for multiple hours or days.
A small LED flashlight that pulls around 20mAh will last for 5 hours.
Your hobby DIY circuit board will last for an hour at least.
An electric acoustic guitar will last for a couple of hours as well.
2 hours to have the battery fully charged from 0%.
Will outlast a 1000 AA Alkalines.
Will save you a 1000 dollars on a single AA battery.
Wireless alternative to the rechargeable batteries.
Re-using and producing less will meaningfully improve the environmental impact. That will directly lead to a lower disposal rate and need for recycling.
After a journey in a thousand miles, I’m happy to return to my initial goal list and see that all the points of the original plan morphed into a product that I would like to have in all my battery-operated devices.
Goal — results check-in
- ☑ Create the first wirelessly rechargeable AA battery
- ☑ Charge it from any Qi wireless power transmitter
- ☑ Recharge with or without taking it out from the device
- ☑ Build something convenient and competitive while helping the environment
- ☑ Make it last.
That all excites and motivates me to put another goal for the foreseen future.
☐ Find funds and partners to set up the production
☐ Launch Kickstarter or/and Indiegogo campaign
☐ Make it available for online purchases on Amazon
☐ Bring it offline to the corner stores and gas stations across the country
☐ Scale it through AAA, D, C, 9V battery types
☐ Help brands convert their wired products to the wireless technology
☐ Design a couple more novel batteries and a wireless charger
Your yes or no feedback is important to me to understand the level of interest, thanks!
I invite you to subscribe for the waiting list on our website www.airiona.com
Drop a question or just say hi at firstname.lastname@example.org
to be continued...