Battery size is the main key to look for when you purchase a portable wireless Bluetooth speaker. The Bluetooth speaker needs the power to function like every electronic device. You can check the mAh capacity of the battery of the speaker to get a good quality one. But it is better that you check playtime rather than the battery capacity of the device to get a satisfying purchase of a wireless portable Bluetooth speaker. Portronics wireless Bluetooth speaker has good playtime as well as battery capacity. So you can look it up on the internet.