Introduction
If your cell is currently hot, stop using it. Let it cool. Check your resistance. And remember: When a lithium-ion datasheet says "Max discharge: 35A," it means "At 25°C, with perfect airflow, for 30 seconds, you won't die." For the rest of us, 25A is the new 35A.
5. Summary of "Hot" Risks
- Thermal Runaway Risk: If the cell temperature exceeds roughly 130°C–150°C (usually due to external short circuit, overcharge, or physical damage), the chemical reaction becomes self-sustaining (thermal runaway), potentially resulting in fire.
- Degradation: Sustained operation at the "hot" end of the spec (45°C–60°C) will rapidly degrade the cell's capacity.
- Power Density: At 35A and 3.6V, you are pulling roughly 126 Watts continuously from a single cell the size of your thumb.
- The Heat Curve: At 35A, the internal resistance generates significant Joule heat (I²R loss). The datasheet shows that at this load, the surface temperature of the cell climbs rapidly past 80°C (176°F) within minutes.
Dimensions: Approximately 21.1mm in diameter and 70.4mm in length (Flat top style). Thermal & Safety Characteristics
2. Pressure Vent
- If the cell overheats drastically (thermal runaway), an internal safety valve will rupture (vent) to release gas and prevent an explosion.
- Warning: A venting cell releases hot, toxic gas. If you hear a hissing sound or smell chemicals, move away immediately.
Has anyone else measured surface temps on these at 10A+? Would love to compare notes.
- Critical Threshold: Internal cell temperature exceeds 130°C - 150°C.
- Peak Temperature: In a runaway event, the cell can exceed 700°C.
- Prevention: Never charge unattended. Use a charger with over-voltage protection that stops at 4.20V.
The NCR21700T at a Glance: The Specs that Matter
Before we talk about heat, let us look at the cold, hard numbers from the official Panasonic/Sanyo datasheet.