2 PCS 18650 Battery USB Port with Rechargeable Charger 3800mAh LED Multi-Function Pro After plugging this battery in an alive USB port, the red light will shine and prove it's charging. When the light turn yellow, it has been fully charged. It need around 7 hours to be fully charged and pls not charge it too long while it will influenced the batteries' life The battery keeps in top condition within the temperature from -10 to 40. Only with an alive USB port, it can be charged more than 500 times Suitable for all products powered by 18650 batteries