Ultra-Slim Li-Polymer Pack Doubles Runtime in a Global Smartwatch Line
A tier-one wearable OEM needed more capacity in the same 3.2mm cavity. EPT delivered a custom N-type cell architecture that doubled runtime and scaled to mass production in 14 weeks.
At a Glance
Project snapshot
- Industry: Consumer electronics — smartwatch & hearables
- Challenge: Double battery runtime inside an existing 3.2mm enclosure
- Solution: Custom 3.8V Li-polymer with EPT N-type high-density cell design
- Outcome: 2× runtime, 800+ cycle life, UL / UN38.3 certified at scale
- Timeline: Concept to mass production in 14 weeks
Key outcomes
- Runtime gain
- 2×
- Pack thickness
- 3.8 mm
- Cycle life
- 800+ cycles
- Time to MP
- 14 weeks
The Challenge
The client was preparing a next-generation smartwatch with no room to enlarge the battery bay. Field data showed users abandoning daily charge routines—runtime had become a purchase blocker.
Off-the-shelf pouch cells could not hit the energy-density target without exceeding the mechanical stack-up. The program also required UL 2054 and UN38.3 clearance before holiday retail launch.
- Fixed mechanical envelope — no ID changes allowed
- Target: ≥2× usable runtime vs. previous generation
- Must pass drop, thermal, and shipment safety tests
Our Approach
EPT applied its N-type electrode architecture to maximize active material loading in a custom 55×35×3.8mm pouch. PCM tuning reduced quiescent drain while preserving peak current for GPS and health-sensor bursts.
Parallel pilot lines in Shenzhen validated yield before transferring to high-volume Meizhou production. Every lot was screened through our 36-step QC flow and CNAS-accredited safety lab.
- Custom cell model LP5538038 with matched PCM/BMS
- Iterative DVT with client firmware team on load profiles
- Automated grading for capacity consistency across lots
Results
Production units shipped on schedule for the global retail window. Battery-related returns dropped measurably in the first two quarters post-launch, and the client extended the platform to two additional SKUs using the same core design.
- 2× measured runtime in real-world usage tests
- Zero safety incidents across 1.2M+ units shipped
- Platform reused for earbuds case and fitness band lines
FAQ
Frequently asked questions
- Can EPT design batteries for existing mechanical enclosures?
- Yes. We routinely reverse-engineer around fixed ID constraints and propose cell geometries, PCM layouts, and thermal paths that fit your housing without a full redesign.
- What certifications apply to wearable Li-polymer packs?
- Typical programs require UL 2054 or IEC 62133, UN38.3 for transport, and regional marks such as CE. EPT manages test planning through our CNAS-accredited lab.
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