Fast-Charging Batteries in Wearables: Tiny Devices, Big Innovations
This week we have a special edition on wearable tech from a subject matter expert.
Hi! I am Abhineet Nigam. I am a Senior Battery Engineer at WHOOP, leading the battery subsystem for the company. More about me at my website.
Wearable technology has firmly integrated itself into everyday life. From smartwatches and fitness trackers to wireless earbuds and medical devices, these compact gadgets help us stay connected, improve our health, and manage our daily activities. However, one significant challenge that still persists in the wearable tech world is battery life and the time required to recharge these devices and lose hours of data as they charge slowly on your nightstand (unless you are talking about WHOOP and their on-body charging!).
Fast-charging technology could completely revolutionize the market, allowing users to quickly top up their devices in mere minutes rather than waiting hours for a full charge. Interestingly, and I will talk about this more in the coming sections, many of the innovations enabling this transformation are borrowed from more established sectors such as electric vehicles (EVs), where advancements in fast charging have made impressive strides in recent years.
Let’s get into what to watch out for!
Wearables today are capable of delivering incredible functionality in a small form factor. Devices like smartwatches are equipped with high-resolution displays, health-monitoring sensors, GPS tracking, and many other features - all powered by relatively small batteries. However, most smartwatches today only last for a day or two on a single charge. Apple Watch Ultra, the leader in the smart watch industry, for instance, quotes to provide up to 36 hours of battery life and up to 17 hours of workout use in Low Power.
Fast-charging technology offers a significant solution to this problem. A quick 10-15 minute charge in the morning could power you through your day. For users, this is incredibly convenient, especially in a world where time is increasingly at a premium. Surveys show that 57% of smartwatch owners prioritize improved battery performance, including faster charging, when considering future models. In wearables, faster charging isn’t just a nice-to-have feature - it’s becoming an essential capability. Faster charging also opens up new use cases like sleep tracking, where users no longer need to leave their devices on the charger overnight, or reduces the downtime for medical devices that patients rely on for continuous monitoring.
The challenge, however, is designing a battery and charging system for such small devices. Wearables don’t have the luxury of large batteries or active cooling systems. Pumping high currents into a small battery can lead to overheating or cause rapid degradation of the battery if not carefully controlled.
This is where lessons learned from larger devices, such as electric vehicles, come into play.
The electric vehicle industry has seen remarkable advances in battery technology, particularly in the field of extreme fast charging (XFC). Many electric vehicles today can charge from 10% to 80% in under 20 minutes. In 2023, a UK-based startup, Nyobolt, demonstrated an EV concept car capable of charging its 35 kWh battery to 100% in under six minutes, an achievement comparable to the time it takes to refuel a gasoline car. This innovation relies on breakthroughs in materials such as advanced anodes, high-performance electrolytes, and robust thermal management- all of which directly inform battery research for devices of all sizes.
Additionally, China’s BYD recently unveiled a new supercharging platform capable of delivering peak charging speeds of 1,000 kilowatts (kW). This allows EVs to charge enough for 400 kilometers (249 miles) in just five minutes, making it twice as fast as Tesla’s superchargers. BYD is also investing in building over 4,000 ultra-fast charging stations across China. This development has the potential to trickle down to smaller devices.
The fast-charging race is already extending from cars to smartphones. Realme’s 2023 smartphone, for instance, supports 240W charging and can fill a 4,600 mAh battery in just 9.5 minutes. This breakthrough is made possible by innovations such as dual (separate cells joined as a pack) battery cells and cutting-edge cooling technologies.
As battery technology improves, we might one day charge a smartwatch or augmented reality (AR) glasses to full capacity in the time it takes to brew a cup of coffee. To charge a battery quickly without compromising safety or performance, several factors must be optimized: the materials of the electrodes (anodes and cathodes), the electrolyte, battery management systems (BMS), and thermal control.
Electrode Materials
Since fast charging a lithium ion battery involves moving lithium into the anode quickly, focus here looks at anode materials.
The transition from graphite to silicon anodes is a game-changer. Silicon can store up to ten times more lithium ions than graphite, significantly increasing a battery's energy density. This allows wearables to be powered by either smaller batteries or batteries with longer runtime. While larger capacity doesn’t necessarily translate to faster charging, a higher energy density allows for greater usage from a shorter charge. However, silicon anodes pose a challenge: they expand by up to 300% when fully charged, which can cause the electrodes to crack and degrade the battery rapidly. To solve this, researchers have combined silicon with graphite in composite electrodes or used nanostructured silicon in the form of nanoparticles or nanowires. These innovations help mitigate the issues of expansion while improving battery lifespan. Companies like Amprius Technologies have made strides with 100% silicon nanowire anodes, which can charge up to 80% in just 6 minutes.
Heat loss is measured as I²R per unit time. For fast charging applications, as the current is high, the heat produced is high as well as shown by the above equation. To reduce the heat produced, efforts are made to switch to materials that have high conductivity and low internal resistance.
Graphene is known for its excellent conductivity and thermal properties. By integrating graphene into battery electrodes, it is possible to reduce internal resistance, enabling batteries to handle higher charge currents without generating excessive heat. Graphene-based materials are also being used for efficient thermal management, preventing batteries from overheating during fast charging, conducting heat produced away from the battery itself.
Another promising material is niobium-based anodes, which allow for extremely rapid charging. Niobium-tungsten oxide (NWO) anodes, for example, have an open crystal structure that allows lithium ions to move quickly, enabling charge times of just minutes. I mentioned earlier Nyobolt, a company championing niobium-based batteries, who have demonstrated charge times of 80% in under 5 minutes, an ideal fit for wearables where rapid boosts are often more desirable than long battery life.
The Electrolyte
The electrolyte plays a critical role in determining just how fast and how safely a battery can charge. When current is pushed into a cell too quickly, it can lead to lithium plating, a condition where lithium ions deposit as metal on the anode surface instead of intercalating into it. This not only damages capacity but also risks short circuits and thermal runaway.
To prevent this, researchers are engineering next-generation electrolytes and additives that form a stable solid-electrolyte interphase (SEI) layer, protecting the anode and allowing high-rate charging without degradation. These additives act like chemical bodyguards, ensuring ions move efficiently while keeping harmful reactions in check.
Some companies are going beyond the traditional liquid electrolyte entirely. Solid-state batteries (SSBs), which replace the flammable liquid electrolyte with solid materials like ceramics, glass, or polymers. SSBs not only boost safety but also enable thinner, flexible cell formats – perfect for wearables. Importantly, solid electrolytes can support higher voltage operation and faster lithium-ion mobility under the right conditions, making them ideal candidates for future fast-charging devices. Samsung is among the companies actively developing solid-state coin cell batteries aimed specifically at wearables. While the tech is still maturing, the smaller form factor means SSBs may reach mass production in wearables even before they’re fully commercialized in EVs. Globally, companies like Toyota and Samsung have already committed billions toward SSB development, aiming for broad rollout by 2027.
Battery Management Systems
Fast charging isn't just about materials - it’s also about how the battery is managed. Charging algorithms and battery management systems (BMS) are essential to optimizing charging rates while ensuring safety. Modern BMS use adaptive algorithms powered by artificial intelligence to adjust the charging power in real-time. This helps minimize stress on the battery, avoid overheating, and ensure the battery lasts longer. Modern BMS use adaptive algorithms powered by artificial intelligence to adjust the charging power in real-time. This helps minimize stress on the battery, avoid overheating, and ensure the battery lasts longer.
In wearables, where space and power budgets are tight, BMS must be even more efficient and integrated than in larger devices. A typical wearable BMS not only monitors cell voltage and temperature, but may also predict user behavior to time high-current charging sessions safely. Some advanced systems even factor in ambient temperature (e.g. whether the device is charging on a warm surface or in a cool room) and throttle current accordingly. Moreover, modern BMS architectures in wearables often include state-of-health monitoring that tracks battery degradation trends over time, helping to balance charge speed with longevity.
As machine learning becomes more common in embedded firmware, we can expect next-gen BMS to learn individual user patterns, knowing when to use aggressive fast charging and when to hold back. The miniaturization challenge also drives innovation in system-on-chip designs for power management. Several semiconductor companies are now producing ultra-low-power BMS chips with integrated protection features that fit comfortably inside even the most compact wearable enclosures. Combined with external apps and cloud syncing, these systems will make wearables not just fast to charge, but also smarter about when and how they do it.
Thermal Control
Thermal management is also crucial in wearables. While EVs use active cooling systems to manage heat during fast charging, wearables must rely on passive cooling methods. Innovations such as graphene heat spreaders are being explored to efficiently manage heat during charging, ensuring devices don’t overheat and remain safe to use.
These breakthroughs signal that fast-charging wearables are no longer a distant future but an imminent reality. As innovations from the EV world, material science, and battery research continue to converge, we can expect wearables to become more powerful, safer, and faster to charge.
The future of wearables is evolving rapidly, and fast-charging batteries are at the heart of this transformation. Thanks to breakthroughs in silicon anodes, solid-state designs, graphene, and intelligent charging systems, wearables are becoming more efficient, safer, and faster to charge. We can expect the next generation of wearables to charge in minutes and last longer, providing greater convenience and expanding their potential use cases.
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