Battery Applications in Access Cards

Access cards with advanced features (e.g., RFID, biometrics, or e-ink displays) rely on batteries for secure, long-lasting, and compact power solutions. Below is a detailed technical breakdown of battery technologies, use cases, and design considerations for modern access cards:

1. Common Battery Types

**(1) Lithium Coin Cells (CR2032/CR2450)**

• Voltage: 3V.
• Capacity: 200–620mAh (1–5 years standby).
• Advantages:
• Ultra-Compact: Fits into card thickness <3mm.
• Low Self-Discharge: <1% per year.
• Use Cases:
• Basic RFID Cards: Powering passive-to-active RFID conversion.

• E-Ink Display Cards: Refreshing time/date or credentials (e.g., hotel keycards).

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**(2) Thin-Film Lithium Batteries**

• Voltage: 3V–4V.
• Capacity: 10–100mAh (6–12 months active use).
• Advantages:
• Flexible & Lightweight: 0.5mm thickness for bendable cards.
• Custom Shapes: Tailored to card layouts.

• Drawbacks: Limited capacity for high-drain features.

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**(3) Rechargeable Li-Po Batteries**

• Voltage: 3.7V.
• Capacity: 50–200mAh (3–12 months per charge).
• Advantages:
• USB/Wireless Charging: Qi-enabled cards (e.g., NFC charging pads).

• Sustainability: Reduces disposable battery waste.

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2. Performance Comparison

3. Key Design Challenges

1. Size Constraints:
• Card Thickness: Batteries must not exceed ISO/IEC 7810 ID-1 standards (0.76mm–3mm).
2. Power Efficiency:
• Active RFID: Requires <10µA standby, 10mA peak during transmission.
3. Durability:
• Bend Cycles: Thin-film batteries must withstand >10,000 flexes.
4. Security:

• Tamper-Proofing: Prevents battery removal without destroying the card.

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4. Maintenance & Compliance

• Standards:
• ISO/IEC 15408: Security requirements for biometric access cards.
• RoHS Compliance: Restricts hazardous materials in batteries.
• Replacement:
• Non-rechargeable cards: Replace entire card after battery depletion.

• Rechargeable cards: 500+ charge cycles with 80% capacity retention.

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5. Case Studies (Generic Applications)

1. E-Ink Hotel Keycard:
• Battery: CR2450 (620mAh, 3V, 3-year lifespan).
• Features: Displays check-out time, room number.
2. Biometric Access Card:
• Battery: 80mAh thin-film Li (1mm thick, 8-month active use).
• Authentication: Fingerprint scanning + NFC.
3. Wireless Charging Employee Badge:

• Battery: 150mAh Li-Po (Qi charging, 6-month runtime).

6. Future Trends

1. Energy Harvesting:
• RF or Solar Charging: Ambient RF energy (e.g., NFC readers) or micro solar cells.
2. Solid-State Batteries:
• Safer, thinner cells with higher energy density.
3. Biodegradable Batteries:

• Eco-friendly materials for disposable access cards.