The design space for modern smart glasses, smart rings, wearable medical devices, and similar products is extremely limited, yet they require high-performance batteries to support rich functionality. Engineers frequently face a triple challenge during design: compact space, battery life anxiety, and unconventional shapes. Batteries must be extremely miniaturized while meeting requirements for battery life, reliability, and comfort.
Consequently, standard cylindrical or button batteries fall short, often forcing designers to compromise between functionality and endurance. While larger batteries extend runtime, they severely compromise wearability and aesthetics. As industry analysis highlights, “batteries represent the greatest bottleneck” for wearables. Off-the-shelf power solutions inevitably lead to design compromises; true innovation demands multidisciplinary, customized solutions.
Big-Brand Examples: Unlocking Design Innovation by Freeing Battery Space
There are already many industry examples showing how design changes can free up battery space. One well-known case is Apple’s decision to remove the 3.5 mm headphone jack from the iPhone. Apple executive Dan Riccio once stated that the headphone jack was “just a hole filled with air,” taking up valuable space that could be used for the camera, processor, and battery. By removing it, Apple created more room for a larger battery and also improved water resistance.
A similar approach can be seen in Apple’s AirPods lineup. The AirPods Pro 2 charging case uses a dual-cell battery design with a total capacity of about 523 mAh, allowing Apple to better use the remaining internal space and extend battery life. Teardown reports show that by separating the charging circuit and main board into two smaller modules, the internal layout became more compact, resulting in better endurance than a single-cell design.
In addition, many TWS earphone manufacturers are improving battery life through new battery technologies. Advanced lithium polymer solutions, such as ultra-high-density LiPo batteries, achieve higher energy density in very small volumes. Reports show that by using silicon-carbon anodes, ultra-thin foils, and edge-reduction designs, cell capacity can be increased by about 15% within the same volume, improving earbud runtime by 10–30%. At the same time, battery weight can be reduced by more than 10%, and battery sizes can be customized to match the earphone’s structure.
These examples clearly show that custom battery solutions and structural optimization can truly unlock space potential, giving designers more freedom—rather than forcing products to compromise around fixed, standard batteries.
Smart Rings: Curved Batteries Enable Functional Integration
Smart rings are extremely small in size, yet they are expected to deliver advanced functions such as health monitoring, contactless payment, and notification alerts. These applications require continuous power and sensor processing. For a curved, non-rectangular space like a ring, traditional coin cells are simply not suitable in terms of shape. In smart ring products, miniature curved batteries are a true necessity—only curved battery designs can fit into the tight, circular structure of a ring.
For example, ultra-thin curved LiPo batteries are designed specifically for smart rings and can closely follow the inner arc of the ring. Once the custom battery perfectly matches the ring’s contour, more space is freed inside the ring to integrate additional electronics and sensors.
The benefits of custom batteries are clear. Smart rings using curved batteries can achieve longer battery life while remaining lightweight and slim. Ultra-thin curved LiPo batteries fit naturally within the ring frame and sit comfortably against the wearer’s skin. Their high energy density supports longer operating time and reduces charging frequency. Industry analysis further shows that by using advanced materials such as silicon-carbon anodes, battery capacity can be increased by up to 30% without increasing volume. This allows some smart rings to extend battery life from around four days to more than one week.
Smart Glasses: Deep Integration with Custom Ultra-Slim Batteries
Smart glasses must combine optics, audio, and sensing functions, which makes their internal space extremely limited. Industry data shows that most smart glasses use one to four LiPo battery cells, with a total capacity typically in the range of 80–120 mAh, balancing wearing comfort and battery life. For example, Bose smart glasses include a battery of about 110 mAh, while AfterShokz smart sunglasses use a 180 mAh battery. As AR and AI features continue to expand, engineers must use every bit of available space more efficiently.
Custom batteries play a critical role in smart glasses. They can be designed in L-shapes, curved forms, or ultra-narrow strip formats to precisely match the irregular geometry of the frame and temples. For instance, Huawei Smart Glasses 2 adopt a highly integrated design with dual batteries and a dual-layer PCB inside the left and right temples, effectively reducing overall thickness.
Similar solutions are widely used across the industry. Teardown analyses of various smart glasses show that manufacturers often increase battery life by placing multiple small cells symmetrically, typically one battery in each temple. The ultra-narrow lithium battery embedded in the temple area, as shown in typical designs, is specifically engineered for long and slim spaces, maximizing space utilization while still delivering stable power output.
The ultra-narrow lithium polymer battery module developed by BluePower, with a width of only 5mm, is specifically designed for extremely tight spaces such as smart glasses temples. It maximizes space utilization while still delivering reliable and sufficient power.
At the same time, custom batteries also help address system-level challenges such as thermal management. Engineering data shows that each additional battery cell or a more powerful processor in smart glasses generates extra heat, while these devices sit very close to the skin and have very low heat tolerance. Through co-designed irregular battery shapes and thermal structures—for example, placing a heat-spreading layer on the back of the battery—it is possible to achieve higher energy density (such as by using high-silicon battery cells) while reducing heat buildup. This approach significantly improves both thermal performance and overall user comfort.
Medical Wearables: Custom Batteries Ensure Safety and Long Runtime
In wearable medical devices—such as continuous glucose monitors (CGMs), smart patches, and heart rate sensors—batteries must meet extremely high standards for safety and reliability. These devices are often worn for long periods, undergo frequent charge cycles, and remain in direct contact with the skin. Custom batteries can be designed to match the exact form of the device, such as flexible patch batteries or slightly curved cells, allowing them to fit seamlessly against the skin or inside very compact housings.
Industry reports, including those from SERUI, note that custom LiPo batteries are well suited to the ultra-thin and long-life requirements of medical wearables. For example, some smart patches require batteries that sit almost flush with the device enclosure. Custom curved batteries, with their high energy density, can extend monitoring time while reducing charging frequency.
At the same time, a robust Battery Management System (BMS) is essential. Accurate state-of-charge measurement and real-time temperature monitoring are critical for skin-contact devices. These systems help ensure stable operation and provide automatic protection under extreme conditions, such as overcharging or overheating. By customizing the cell shape, chemistry, and battery management as a complete system, medical-grade wearables can meet their strict demands for reliability, safety, and user comfort.
Quantified Improvements Enabled by Customization
Improved space utilization
Custom batteries can be designed in curved, C-shaped, L-shaped, or other irregular forms to perfectly match the device enclosure. For example, batteries can be made as thin as 0.5 mm and as narrow as 5 mm, far smaller than standard cells. Within the same overall volume, space utilization is maximized with no “dead space” left unused.
Higher energy density
By adopting advanced materials such as high-voltage electrolytes and silicon–carbon anodes, custom batteries can increase energy capacity by 15–30% without increasing size, significantly extending runtime.
Longer cycle life and higher reliability
High-quality custom batteries are optimized in design and validated through strict testing, achieving cycle life of 1,000 cycles or more. In AI glasses, for example, optimized batteries show only about 10% capacity degradation after 300 cycles. Custom batteries for medical wearables are also often produced under certified quality systems such as ISO 13485, ensuring stable performance and high safety for every cell.
Flexibility in custom solutions
Battery voltage (such as 4.2 V or 4.35 V) and fast-charging rates (3C–5C) can be customized, with high-voltage versions available for mass production. For smart rings and skin-mounted devices, this means sufficient voltage and faster charging can be achieved even within extreme size constraints, improving overall user experience at the system level.
Conclusion
In summary, custom battery design is a system-level engineering challenge that requires close collaboration across multiple disciplines, including electrochemistry, mechanical design, and firmware algorithms. As a technical team with extensive experience in wearable battery development, BluePower deeply understands and addresses real-world customer challenges—delivering batteries that provide reliable power, fast charging, high energy density, and long cycle life, while remaining “invisible” within the product structure and precisely aligned with ergonomic requirements.
If you are developing a wearable product with highly constrained size, form factor, or power budgets, we welcome you to contact BluePower for early-stage technical discussions. They provide integrated, engineering-grade solutions covering cell development, custom-shaped packaging, and BMS firmware tuning, ensuring that every design is thoroughly validated. This early collaboration helps product teams gain greater design freedom and reduce engineering risk from the very beginning.
Through proven, practical engineering solutions, BluePower helps customers overcome battery limitations and achieve the optimal balance between design and performance—allowing wearable devices to truly follow the principle of “battery serving the design,” rather than design being constrained by the battery.
