I have a Rexton BLU RCU remote and I assume that the Siemens TEK is similar.
My remote was getting low on battery so I connected the mini-usb on the bottom to a usb port on my puter. It didn’t charge. I connected the mini-usb to a generic 120v to usb adapter - no charge. Only when I connected the mini-usb to 120 using the adapter included with the BLU RCU kit did the remote charge, and as it charged it showed the “charging” symbol on its screen.
Anyone else see this type behavior??