Hello, the Toshiba 4TB 2.5" Canvio Ready (HDTP340EK3CA) USB 3.0 external drive does not require an external battery. It takes all the power it needs to work directly from the computer through the USB cable. So there is no battery inside the device, so it won't work when the battery runs out? There is no such situation. It runs as soon as you connect it to your computer and stops when you disconnect it from the computer. If you have any other questions, we will be happy to help. We wish you a nice day.