Firedog,
I remember the fight to open this snap ring, as far as I remember I managed to open snap ring without removing the collar,
display/controller gets 5V for powering its circuit board from battery electronics over comm cable.
you have to check continuity of all wires of this comm cable with ohmmeter , complete from pins inside display/ctr. to pins on processing /upper/ board of battery electronics while wobbling comm cable around.
you must open display/ctr.
BUT BEFORE THAT.
another possibility are tactile switches of display/ctr.. - I had exact failures.
oxidation builds up on switches contacts due to rain or washing, if you have such oxidation on POWER UP switch it shorts and acts as if you pushed it.

Motor has nothing to do with display/ctr. going blank.
why do you want it to open it?
with edrive like EPLUS you must have spare parts like display/ctr.
I have spare display/ctr. matched to motors for my winter and my summer EPLUS
Rick Ruggiero would be happy to sell parts to you.