2-Pack 21700 Rechargeable Battery, 4000mAh 3.6V Flat Top, High Drain 40A for Flashlights, Headlamps Devices & High-Power Applications

Key Features

• 40A Continuous High Drain – Handles extreme current loads without dangerous voltage sag.

• 4000mAh Verified Capacity – Real tested capacity; ideal balance of runtime and power.

• Flat Top Design – Low contact resistance, fits most 21700-compatible devices.

• Low Internal Resistance (~12-15mΩ) – Less heat, more efficient energy transfer.

• A-Grade Cells – Capacity-matched and inspected, no recycled junk.

• 2-Pack Convenience – Two cells ready to rotate or use in dual-battery setups.

• Long Cycle Life – 500+ charge cycles with ≥70% capacity retention.

• Built-in Safety – Pressure relief vent and CID for critical fault protection.

Parameters

Applications

• High-Lumen Flashlights – Sustains turbo mode for tactical, search, and EDC torches.

• Headlamps – Powers high-output caving, cycling, and rescue headlamps.

• Power Tools – Rebuild cordless drill and impact wrench packs needing 40A surges.

• DIY Projects – Use in custom power banks, portable amps, or small e-mobility packs.

FAQ

Q: Are these protected batteries?
A: No. They are unprotected flat-top cells for maximum discharge performance. Use only in devices with low-voltage cutoff or add an external protection circuit. Never short circuit.

Q: Will they fit my flashlight?
A: If your flashlight accepts unprotected flat-top 21700 cells, yes. Check that the positive contact can reach a flat terminal. Devices designed for button tops may need a magnet spacer (use with caution).

Q: What charger is required?
A: A Li-ion charger supporting 3.6V/3.7V cells, 21700 size, with CC/CV and 4.2V cutoff. Recommended brands: Xtar, Nitecore, Gyrfalcon. Do not use NiMH chargers.

Q: Is the 4000mAh real?
A: Yes, tested at 0.2C discharge. At high currents (e.g., 20A), usable capacity is slightly lower (~3800-3900mAh), which is normal.

Q: Can I mix with other cells?
A: Never mix old and new cells or different models in series. Always use identical, age-matched batteries.