After you finished the assembly of the case, look for the reset button on the PCB of the geiger counter, located near to the USB port.

Push the reset button of the geiger counter with your finger or with a plastic spudger to reset your device to the factory defaults (this step is necessary after battery replacement).

Reinsert the USB port cover into the bottom side of the geiger counter.

After you set the date and time and configure the datalogging settings, your device is fully functional.

Check the battery voltage on the screen of your device.

Because geiger counters are test equipments, after a battery replacement you should check the correct function of the device and you should also check the accuracy of the device with a known test source.