1/2 C Batteries (Category Guide)

1/2 C batteries deliver reliable power in tight spaces for sensors, medical equipment, alarms, and backup systems. This guide explains sizes, chemistries, compatibility, and how to choose the right cell for your device.

Size, Names, and Equivalents

Typical dimensions: ~17 mm diameter x 33–34 mm length. Common names and part codes include 1/2 C, 1/2C, 17335, CR17335 (3.0V lithium manganese dioxide), and ER17335 (3.6V lithium thionyl chloride).

Physical fit notes:

• Similar size to CR123A (also ~17 x 34.5 mm). Physical fit does not guarantee electrical compatibility.
• Not the same as a standard C battery (much longer) or a 16340 Li‑ion (3.6–3.7V rechargeable).

Chemistry Comparison

Chemistry	Typical Marking	Nominal Voltage	Typical Capacity	Operating Temp	Shelf Life	Best For
Lithium Thionyl Chloride	ER17335	3.6V	1.7–2.4 Ah	-55 to +85°C (some to +125°C)	10+ years	Low‑drain, long‑life sensors; wide temperature extremes
Lithium Manganese Dioxide	CR17335	3.0V	1.3–1.6 Ah	-20 to +60°C	7–10 years	General electronics, cameras, alarms with moderate pulse needs
Nickel‑Metal Hydride (rechargeable)	1/2 C NiMH	1.2V	1.0–2.0 Ah	0 to +50°C (charge); -10 to +50°C (discharge)	N/A (self‑discharge; recharge as needed)	Frequent‑use devices where recharging is practical

How to Choose

• Match voltage first: Use 3.6V ER17335 only if specified; many consumer devices expect 3.0V CR17335/CR123A. NiMH (1.2V) is only for devices designed for low voltage packs.
• Load profile:
  • Very low average current (µA–mA) with occasional pulses: ER17335 (bobbin type). For high pulses, add a pulse‑cap/HLC or choose a pulse‑optimized cell.
  • Moderate pulses (cameras, lights, alarms): CR17335 (3.0V) often better pulse delivery.
  • Frequent use and easy access to charging: 1/2 C NiMH.
• Temperature: Outdoors or industrial extremes favor ER17335. Indoor general use can use CR17335.
• Terminations and fit: Select button‑top vs. flat‑top, solder tabs, axial leads, or PCB pins to match the holder/PCB. Verify polarity and height.
• Service life vs. cost: For multi‑year deployments, ER17335’s longevity often lowers total cost of ownership.

Runtime Planning (Quick Math)

Estimated runtime (hours) ≈ usable capacity (mAh) ÷ average load (mA). Apply a 0.7–0.9 factor for pulse losses and environment.

• Example 1: 1.8 Ah ER17335 powering a 50 µA sensor: 1800 mAh / 0.05 mA ≈ 36,000 h ≈ 4.1 years. Real‑world: 3–4+ years after temperature and pulse overhead.
• Example 2: Device draws 200 mA for 1 s each minute plus 100 µA standby: average ≈ (200 mA × 1/60) + 0.1 mA ≈ 3.43 mA. With a 1500 mAh CR17335: 1500 / 3.43 ≈ 437 h (~18 days). Pulses may require a buffer capacitor.

Compatibility and Safety

• Not interchangeable with C cells.
• CR123A vs. 1/2 C: Similar size, but voltage and pulse capabilities can differ. Confirm the exact chemistry and voltage your device specifies.
• 16340 Li‑ion is not a drop‑in: 3.6–3.7V rechargeable; only use if the device explicitly supports Li‑ion.
• Do not charge primary lithium cells (CR/ER types). Risk of fire or rupture.
• Prevent short circuits; store cool and dry (~20°C). Recycle at approved drop‑offs.

When to Choose Each Type

• Choose ER17335 (3.6V) if: long life (years), low average current, cold/heat extremes, remote sensors, meters. Add an HLC/capacitor for radio bursts.
• Choose CR17335 (3.0V) if: consumer electronics or alarms specify 3.0V, moderate pulse loads, standard indoor temperatures.
• Choose 1/2 C NiMH (1.2V) if: you can recharge frequently and the device is designed for 1.2V cells or packs.
• Avoid: mixing chemistries in the same device; substituting 3.6V for 3.0V without confirmation; using Li‑ion where not supported.

FAQs

• Are 1/2 C and CR123A the same? They are similar in size. CR123A is typically 3.0V (LMnO2). Some 1/2 C cells are 3.6V (Li‑SOCl2). Always match the specified voltage and chemistry.
• How long do ER17335 cells last in sensors? Commonly several years. Shelf life is 10+ years; actual service life depends on average current, pulses, and temperature.
• Why does my device reset on transmit? High pulse current can cause voltage sag. Use a pulse‑rated cell or add a buffer capacitor/HLC; ensure low contact resistance.
• Can I replace a 3.0V CR17335 with a 3.6V ER17335? Only if the device specifies 3.6V tolerance. Otherwise you risk damage.
• What termination should I pick? Use button‑top for holders; solder tabs or axial leads for permanent installations; match the original battery’s style.