🔋 About the Hongli 18650 3.7 V 1200 mAh Li‑Ion Cell

• Form Factor: 18650 cylindrical cell (≈ 18 mm diameter × 65 mm length) 
• Nominal Voltage: 3.7 V (max charge ~4.2 V) 
• Capacity: 1200 mAh (typical around 1210 mAh, 4.44 Wh)
• Internal Resistance: Less than 60 mΩ (often <1 Ω in some listings) 
• Cycle Life: Around 300 to 500 cycles depending on vendor 
• Weight: ~34–38 g per cell
• Charge/Discharge: Usually rated at 0.2C standard charge (240 mA), up to 0.5–1C rates (600–1200 mA)

⚙️ Usage & Safety Tips

• Pair this cell with a proper charging module (e.g. TP4056 or BMS) to control overcharge and discharge cutoff voltage.
• It’s best to match cells in the same pack in voltage and capacity.
• Handle storage/installation space carefully—Lithium-ion cells may swell slightly over time; ensure there's room without tight compression .
• Always use devices benefiting from external protection circuits (if the battery doesn’t include internal protection).