Sub-C Batteries (Category Guide)

Sub-C batteries are high-drain, 1.2V rechargeable cells most often assembled into packs for RC vehicles, cordless tools, and robotics. This guide explains how to choose the right Sub-C cells and packs, what specs matter, and how to charge and care for them safely.

Quick Specs

• Size: approximately 22–23 mm diameter × 42–44 mm length (smaller than C cells)
• Chemistry: Nickel-Metal Hydride (NiMH) or Nickel-Cadmium (NiCd)
• Nominal voltage: 1.2V per cell
• Typical capacity: NiMH ≈ 1500–3000 mAh; NiCd ≈ 1200–2000 mAh
• Discharge capability (typical): general-purpose 3–10A; high-discharge variants 10–30A (check datasheet)
• Common pack voltages: 6 cells (7.2V), 7 cells (8.4V), 10 cells (12V)

When to Choose Sub-C

• Use if: your device draws high current (tools, RC, robotics) and expects NiMH/NiCd packs.
• Use if: you need rugged, cycle-tolerant cells with simple charging compared to lithium packs.
• Avoid if: you need maximum energy density or lowest weight—consider Li-ion/LiPo packs instead.
• Avoid if: your device requires single C cells—Sub-C are smaller and not a drop-in replacement.

How to Select the Right Sub-C

1. Match chemistry to your device
   • NiMH: Higher capacity, lower environmental impact. Good default choice for most modern packs.
   • NiCd: Very robust and tolerant of high discharge and abuse, but lower capacity and contains cadmium. Recycle responsibly and check local restrictions.
2. Choose capacity vs. discharge
   • Higher mAh = longer runtime, but high-discharge cells may trade some capacity for current capability.
   • For RC racing or power tools, prioritize high discharge rating; for light-duty robots, prioritize capacity.
3. Decide on cell format
   • With solder/spot-weld tabs: Recommended for building packs. Avoid soldering directly to bare cells.
   • Prebuilt packs: Simplifies assembly and ensures balanced cells and proper wiring.
4. Confirm fit and connectors
   • Check bay size; Sub-C packs are bulkier than AA/AAA.
   • Match connectors (e.g., Tamiya, Deans/XT60) and wire gauge to your device’s current draw.
5. Check operating conditions
   • Verify charge/discharge temperature ranges (typical discharge -10 to 50°C; charge 0 to 40°C).
   • If continuous heavy use, pick cells with published internal resistance and cycle-life data.

Common Pack Setups and Rough Runtime

Runtime (hours) ≈ Capacity (Ah) ÷ Average load (A). Real-world results are often 70–85% of the math due to heat and voltage sag.

Tip: If your average current halves, runtime roughly doubles. Always verify against the device’s typical current draw.

Charging and Care

Charging

• Use a charger designed for NiMH/NiCd with proper termination.
• Standard charge: ~0.1C for 12–14 hours (e.g., 3000 mAh → 300 mA).
• Fast charge: 0.5–1C with -ΔV detection and temperature monitoring. Do not fast-charge cold (<0°C) or hot (>40°C) cells.
• Avoid long-term trickle charging; top off before use instead.

Storage

• Store cool and dry (~20°C/68°F). Avoid leaving fully depleted.
• NiMH self-discharge over weeks; expect a top-up after storage.
• NiCd: occasional full discharge/charge cycles can mitigate “memory” effects, but avoid deep discharge in NiMH.

Assembly & Handling

• Prefer cells with welded tabs; spot welding is safer than soldering directly.
• Use cells of the same brand, age, and capacity when building packs.
• Prevent shorts during transport and assembly; insulate exposed tabs.

Pros and Cons

Pros

• High current delivery for tools and RC applications
• Rechargeable with robust cycle life
• Simple battery management compared to many lithium packs

Cons

• Lower energy density and heavier than lithium alternatives
• NiCd contains cadmium and requires special recycling
• Not physically or electrically interchangeable with C cells

Alternatives

• Li-ion/LiPo packs: Higher energy density and lighter weight; require specific chargers and protection/BMS; may not be drop-in replacements.
• Alkaline C cells: 1.5V single-use cells with lower current capability; not suitable replacements for Sub-C packs.

FAQ

• Are Sub-C and C batteries the same? No. Sub-C are smaller and typically 1.2V rechargeable cells intended for packs; C cells are larger and often 1.5V (alkaline).
• Can I mix NiMH and NiCd in the same pack? No. Mixing chemistries or capacities leads to imbalance, overheating, and reduced lifespan.
• How many cycles will I get? NiMH often deliver hundreds of cycles; NiCd can be similar or higher with proper care. Actual life depends on depth of discharge, heat, and charging method.
• Do I need matched cells for RC or high current? Recommended. Matching capacity and internal resistance improves performance and pack balance.
• Can I fly with Sub-C packs? Typically yes in carry-on; insulate terminals and follow airline rules. Check current regulations before travel.

Recycling and Safety

• Recycle all spent NiMH and especially NiCd cells at approved facilities.
• Do not crush, short, or incinerate. Stop using cells that overheat, vent, or show damage.
• Follow local regulations; some regions restrict consumer NiCd sales and disposal.