18650 3.65V 3500mAh Lithium-Ion Battery (12.77Wh) - Flat Top High Capacity Cell

FREQUENTLY ASKED QUESTIONS (FAQ)

1. What does "18650" mean? It is the standardized physical size code for the battery. "18" means it is 18mm in diameter, and "65" means it is 65mm long. The "0" means it is cylindrical.

2. Is 3500mAh really possible in this size? Yes! 3500mAh is generally considered the current maximum physical limit for the 18650 chemical form factor using modern, high-end lithium-ion technology.

3. Is this a flat top or button top battery? This is a flat top battery. The positive terminal is flush and does not protrude above the casing.

4. Will this fit in a device that requires a button-top battery? Often, no. If a flashlight has plastic reverse-polarity guards around the positive contact, a flat-top battery won't be able to touch the metal connection point.

5. Does this battery have a built-in protection board (BMS)? No. This is an "unprotected" raw cell. You must use an external BMS board or plug it into a device with a built-in low-voltage cutoff to prevent over-discharging it.

6. Can I solder wires directly to the top and bottom of this battery? NO. Applying the high heat of a soldering iron directly to the steel casing will damage the internal chemistry and can cause the battery to vent or explode. You must use a dedicated battery spot-welder, or use a spring-loaded 18650 battery holder.

7. What is the nominal voltage? The nominal (average operating) voltage is roughly 3.6V to 3.7V.

8. What is the voltage when it is fully charged? A fully charged 18650 will read exactly 4.2V on a multimeter.

9. How low can I safely drain this battery? You should never let an unprotected 18650 drop below 2.8V. Draining it further will cause permanent chemical damage and severely reduce its 3500mAh capacity.

10. What does "discharge at 0.2C" mean? "C" is the total capacity. 0.2C means 20% of 3500mAh, which is 700mA. Drawing roughly 700mA continuously is the optimal efficiency rate to get exactly 3500mAh of runtime out of the cell.

11. Can my project draw more than 700mA? Yes. 18650 cells handle high currents very well. However, running it under a heavy, continuous load (like 3 Amps to 5 Amps) means you may extract slightly less total capacity than the 3500mAh rating due to voltage sag.

12. How do I charge this? You must use a dedicated 18650 lithium-ion charger cradle, or an integrated 4.2V lithium charging circuit module (like the TP4056).

13. Can I wire three of these together to get 11.1V? Yes. Placing three cells end-to-end (in series) gives you a 3S pack. However, you must wire them through a 3S BMS protection board to ensure they charge safely.

14. Can I wire two together to get 7000mAh? Yes. Wiring them side-by-side (positive to positive, negative to negative) creates a parallel pack, keeping the voltage at 3.65V but doubling the massive capacity to 7000mAh.

15. Can I mix this 3500mAh battery with a 2000mAh battery in a custom pack? Absolutely not. Never mix batteries of different capacities, different brands, or different ages in the same series or parallel circuit. The weaker battery will be over-stressed, destroyed, and could catch fire.

16. What is the white ring on the top for? The white ring is an insulator. It prevents the positive center terminal from short-circuiting against the outer edge of the top face, which is connected to the negative casing. Do not remove it.

17. What should I do if the plastic wrapper tears? The entire metal cylinder under the wrapper is the negative terminal. If the wrapper tears, the side of the battery can easily short-circuit against a metal enclosure. Stop using it immediately and re-wrap it using custom 18650 PVC heat shrink tubing.

18. Is this battery waterproof? No. Keep it away from water and extreme humidity.

19. Why does the picture show a blue battery, but mine is red/green? Battery manufacturers frequently change their PVC wrapper colors depending on the production batch. The color of the wrapper does not affect performance.

20. How should I store this battery if I am not using it for months? Do not store it at 100% (4.2V) or 0% (dead). Store it in a cool, dry place at a "storage charge" of roughly 3.7V to 3.8V to significantly prolong its overall lifespan.