Hi Kit
(The Ghost Who Walks)
I don't really have an answer for you, but, a suggestion is put a voltmeter on your battery.
Check the voltage with nothing connected, then try to power up. While powering up and trying to move the scope, see if the voltage drops significantly.
Just possibly, your battery will test OK with no load attached, but, if it is failing, it may have too low a voltage while the motors are pulling a current.
This
might give the error message you are seeing
You could also try unplugging all the internal cables and re-plugging them. Just might be a loose contact somewhere.
Good luck
Philip