You can check the battery status of your trackpad using the Logitech Preference Manager (LPM) software (compatible with Mac OS 10.6.8 or later).
NOTE: If you don't already have Logitech Preference Manager installed, you can download it. See answer 360023412313 for instructions.
To check the battery status of your trackpad:
Launch the Logitech Preference Manager software.
Apple Menu > System Preferences > Logitech Preference Manager
Hover the cursor over the desired icon on the device selection screen to view the current battery and connection status.
NOTE: A black battery icon indicates a usable battery level. A red icon indicates that battery level is low.
NOTE: The device selection screen only appears if multiple LPM-configurable devices are connected to the Mac.
Click the device icon to launch the settings window for that device.
NOTE: If the trackpad is the only LPM-configurable device connected to the Mac, the settings window for that device will launch automatically.
The trackpad's battery status is shown at the bottom left of the settings window.