Use a charger of at least 5V / 1A rating, and a maximum of 5V / 3A* to charge Beosound Explore. Please refer to the article What do the indicator lights on Beosound Explore mean? for information about the battery level status.
*Accepts up to 5 V / 3 A (15 W). You can safely use a higher‑wattage USB charger, but the product will draw a maximum of 15 W.