• The "4.2V Full" Rule: While these batteries are labeled as "3.7V" (nominal voltage), a healthy, fully charged Li-ion battery should measure exactly 4.2V on a multimeter. If your charger stops at 4.1V, it is a safety feature to extend cycle life; if it goes above 4.25V, disconnect it immediately.

• Polarity Check: CRITICAL: Most basic 18650 chargers do not have "Reverse Polarity Protection." Always ensure the positive (+) end of the battery (the end with the small indent or button) matches the (+) mark on the charger. Inserting them backward can cause the charger or the battery to overheat rapidly.

• USB Power Source: For the fastest charging speeds, use a USB wall adapter rated for at least 2A (2000mA). If you plug the charger into a low-power laptop USB 2.0 port, the charging time will be significantly longer because the port cannot supply enough current for two cells.

• Heat Monitoring: It is normal for the batteries to feel slightly warm during the bulk charging phase. However, if a battery becomes too hot to touch, the internal resistance of the cell may be too high (indicating an old or damaged battery), and it should be disposed of safely.

• Avoid "Deep Discharge": To keep your 18650s healthy, try to recharge them before they drop below 3.0V. Standard chargers may sometimes fail to "wake up" a battery that has been drained down to 0V.

Package Includes

• 1 x 3.7V Dual 18650 Rechargeable Lithium Battery Charger

Disclaimer: Never leave lithium batteries charging unattended. Do not attempt to charge non-rechargeable batteries (like Alkaline or Zinc-Carbon) in this device. Ensure the charger is kept away from flammable materials and moisture. Use only with high-quality 18650 cells to ensure safety and performance.

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