Lithium Battery Design for Patch-Type Wearable Devices MOTOMA Wearable Smart Patch Battery

In the development of patch-type wearable devices—such as continuous glucose monitors, skin sensors, and medical patches—the battery is often underestimated, yet it is one of the hardest components to get right. It defines not only battery life, but also wearing comfort, safety, and the overall mechanical design of the product.

1. Space and Form Factor: The Battery Must “Disappear” into the Product

For mechanical engineers, the first constraint of a patch device is not capacity, but space.

These products usually require an overall thickness of less than 2 mm. Traditional rigid batteries are difficult to integrate and often create a noticeable foreign-body feeling on the skin. As a result, ultra-thin pouch lithium polymer batteries or flexible solid-state batteries have become the preferred choice. They can bend slightly with the patch and conform better to the skin, making the device almost unnoticeable during wear.

From an integration perspective, more designs are moving toward deep integration with flexible printed circuits (FPC). SMT-compatible miniature batteries, or even battery designs embedded directly into the flexible circuit, help maximize the use of extremely limited space.

2. Energy Density and Operating Time: Maximizing Runtime in a Tiny Volume

Patch devices typically have modest power consumption, but their runtime requirements are very strict.

Disposable patches often need to operate continuously for 7–14 days, while reusable patches usually require 3–5 days of operation on a single charge. This places high demands on volumetric energy density, with industry targets commonly exceeding 400–600 Wh/L.

At the same time, low-power communication technologies such as BLE and NFC are standard. This makes low self-discharge a key requirement, ensuring predictable and stable battery performance over long wear periods.

3. Recharging Strategy: Charging Is Not the Only Option

Not all patch devices require rechargeable batteries.

For long-term monitoring products, rechargeable lithium batteries remain the mainstream solution, with cycle life typically expected to exceed 500 charge–discharge cycles. In contrast, some disposable medical patches benefit from primary battery solutions, which simplify system design by eliminating charging circuits and post-use recovery concerns.

In higher-end products, wireless charging via Qi or NFC is becoming increasingly common. Removing physical connectors significantly improves water resistance, allowing designs to reach IP67 or even IP68 ratings—an important advantage for devices worn continuously and exposed to water during daily use.

4. Temperature Range and Thermal Management: An Invisible Safety Boundary

Patch devices operate in a very specific environment—direct contact with the human body.

The battery must maintain stable voltage output within approximately 30 °C to 42 °C, corresponding to skin surface temperatures. During charging, temperature rise is usually required to stay below 2 °C to avoid skin irritation or discomfort. In addition, batteries must tolerate storage and transportation conditions ranging from −20 °C to 60 °C, placing further demands on materials and manufacturing processes.

5. Safety and Compliance: A Non-Negotiable Baseline

Because patch devices remain in direct contact with skin for extended periods, battery safety cannot be compromised.

Packaging materials must pass ISO 10993 biocompatibility testing to ensure non-toxicity and non-sensitization. From a mechanical safety standpoint, the battery should not ignite, leak, or fail dangerously when subjected to compression, bending, or accidental puncture—one reason why solid-state and semi-solid technologies are gaining attention.

Ultra-miniature protection circuits are also essential to prevent overcharge, over-discharge, and short circuits, ensuring controlled behavior under all operating conditions.

6. Typical Specification Trends (Reference Range)

• Battery type: Ultra-thin lithium polymer / flexible or thin-film solid-state batteries
• Thickness range: 0.4 mm – 1.5 mm
• Nominal voltage: 3.7 V – 3.85 V
• Capacity range: 10 mAh – 100 mAh (depending on size)
• Safety standards: IEC 62133, UL 1642, UN 38.3
• Waterproof rating: IP67 / IP68 (depending on system design)

In applications with such high integration and safety requirements, engineering experience often matters more than individual specifications.

MOTOMA lithium polymer batteries have been widely applied in patch-type wearable and medical-grade devices, with many proven success cases. MOTOMA offers ultra-thin custom designs, consistent mass-production quality, and comprehensive safety and certification support. From early-stage mechanical coordination to stable large-scale production, MOTOMA focuses on the overall product perspective—helping customers achieve practical, verifiable solutions that balance space, runtime, and safety.