Apple Wireless Keyboard and Mouse No Longer Work

Over the weekend I upgraded my iMac from High Sierra to Mojave. After the upgrade my Apple wireless Keyboard and Mouse no longer work. On the sign-in screen it says no keyboard can be found. I have changed batteries in the keyboard and tried to reset (quickly flashing light) but the computer will not acknowledge the device.

In order to log-in I borrowed a USB keyboard and mouse and was able to get into the system. Both devices show up in the list of usb devices and my computer would connect but still nothing happens. I then went into Bluetooth settings and removed the devices. They both immediately showed back up in the list of devices without me touching the device. Once they reappeared, I tried to connect to the keyboard which again would show as connected but would not display anything on the screen. After a few minutes the device would then show disconnected.

Any ideas on the problem and how to solve.