Consider selecting the Battery Saver option in the Preferences menu to Pause the VPN when the device screen is blanked. This will cause the VPN to disconnect when the screen is blanked and automatically reconnect when the screen becomes visible again. While this option can extend battery life, it should not be used if you have apps running in the background that require continuous access to the internet via the VPN (such as a new email notifier).
Note that if you select both the Battery Saver and Seamless Tunnel options, you will block any app from reaching the internet while the VPN is active but the device screen is blanked. This can be useful for additional energy savings, as long as you don't have any background apps that need constant internet access.