Ring doorbell - 100% charged, rapid flashing blue light

Hi there all.Just installed a standard Ring Doorbell (gen 2) I've hardwired it using the USB cable directly into the mains. It charges fine and works perfectly, but when it gets to 100% charge the blue light flashes (every 0.5 second) lighting up my entire doorway! When I unplug the cable, it stops flashing...Is there anyway to stop it flashing once its fully charged? Or should I not use the USB cable to hardwire it in, and instead get a main kit and connect it on the two terminals on the back?Thanks