Lithium thionyl chloride (Li-SOCl2) batteries, commonly identified by the ER series, are widely used in smart meters, IoT devices, industrial sensors, and critical backup systems. When selecting an ER battery, you may notice suffixes such as M, H, or S added to the model number. These suffixes indicate important differences in battery structure and discharge capability.
Understanding what these suffixes mean helps engineers and product designers choose the correct battery for performance, lifetime, and reliability.
What Do M / H / S Suffixes Mean?
In most manufacturers’ naming conventions, the suffix letters describe the electrode construction and the current capability of the cell. While exact definitions may vary slightly by brand, the following meanings are widely accepted across the industry.
S Suffix – Standard (Bobbin Type)
The S suffix represents a standard, bobbin-type Li-SOCl2 battery. In many cases, the “S” is omitted and the cell is simply labeled as ERxxxx. Such as ER14505, ER17505.
- Bobbin-type construction
- Highest energy density
- Very low self-discharge (often ≤1% per year)
- Low continuous and pulse current capability
- Extremely long service life (10–20 years)
Typical applications: smart electricity meters, water meters, gas meters, low-power IoT sensors, RTC and memory backup systems.
M Suffix – Medium-Rate (Spiral Type)
The M suffix indicates a medium-rate, spiral-wound Li-SOCl2 battery. The spiral (jelly-roll) electrode structure significantly increases the active surface area, allowing higher current delivery.
- Spiral-wound construction
- Lower internal resistance than bobbin type
- Higher continuous and pulse discharge current
- Moderate capacity compared to standard ER cells
- Faster voltage recovery during pulse loads
Typical applications: smart meters with NB-IoT, GPRS, or LTE-M communication, GPS trackers, industrial wireless sensors, alarm and security systems.
H Suffix – High-Rate / High-Power (Advanced Spiral Type)
The H suffix refers to a high-rate or high-power Li-SOCl2 battery. These cells use an optimized spiral structure designed to deliver very high pulse currents.
- Advanced spiral electrode design
- Very low internal resistance
- Excellent performance under heavy pulse loads
- Lower capacity compared to M and S types
- Shorter service life in ultra-low-current applications
Typical applications: military and defense equipment, emergency beacons, high-power industrial communication devices, critical alarm systems.
Comparison of S, M, and H Types
| Type | Structure | Capacity | Pulse Current | Service Life | Best Use Case |
|---|---|---|---|---|---|
| S (Standard) | Bobbin | Highest | Low | Longest | Long-life, low-power devices |
| M (Medium-rate) | Spiral | Medium | High | Long | Wireless IoT and smart meters |
| H (High-rate) | Advanced spiral | Lower | Very high | Shorter | Heavy pulse and critical systems |
How to Choose the Right Suffix
Selecting the correct ER battery suffix depends on your device’s current demand and expected operating life:
- Choose S if your device consumes microamp-level current and requires the longest possible battery life.
- Choose M if your application includes wireless communication and moderate pulse currents.
- Choose H if your device demands frequent or very high current pulses and power delivery is more critical than capacity.
Conclusion
The M, H, and S suffixes in ER series Li-SOCl2 batteries are not just naming details; they define how the battery performs in real-world applications. By understanding these differences, designers can ensure optimal performance, safety, and long-term reliability in smart meters, IoT devices, and industrial systems.