Your Rugged Pro Connect does not have an internal battery, nor does it connect to your iPad via Bluetooth. It receives its power directly from the iPad when the iPad is installed in the case and attached to the keyboard. It also requires a physical connection between the keyboard and the iPad to function.
To establish the initial connection between the two devices, simply insert your iPad while in the case it into the keyboard hinge and restart your iPad. Once the initial connection is established in this way, whenever the iPad is removed and reattached to the keyboard, it should send power to the keyboard immediately.
If you are seeing the power connection being lost after the iPad goes to sleep, be sure your iPad is running iPadOS 16.1. Once the OS has been updated, power cycle the iPad, and the connection will again remain stable.
For instructions on how to install your iPad into the case, click here.