Hello Dear, The speaker has an issue with battery voltage. It has an overall Battery of 7.4 V ( not sure if they connected battery in series by mistake). Please charge it with 9V charger. The charger output has to be converted to USB type to match speaker charger input. I used 9V ( 600mA) charger . It fully charged my Speaker in around 4 hours. ( Normally USB chargeable battery are 3.7V . because They have connected two 4000mAH LI -ion battery in series. So standard USB charger cant charge it. ) Other option could be to use Motorola turbo charger ( I have not tested this option). It has below rating. It should also work , and possibly charge very fast too. Turbo charger output: - Standard: 5V / 1.67A (8W) - TurboPower: 9V / 1.67A (15W) - TurboPower: 12V / 1.2A (15W)