It is important to disconnect the USB cable before you install or change batteries.
If the USB cable remains connected, the logger expects to communicate with the PC. In this mode, the logger cannot go into low-power sleep mode and draws down the batteries. Also, there may be communications problems when a PC and USB cable are reconnected.
If your logger shows these symptoms, remove and replace the batteries (with the USB cable disconnected). Once batteries are in place, you can freely connect and disconnect the USB cable.