Captain reported FMS and display failures in flight with numerous additional systems failures. The flight crew requested vectors and made an air turn back and landed at the departure airport.

Narrative

After takeoff and climbing IFR to cleared 11;000 ft. on heading 295 ex ZZZ Runway XX into gusty conditions and moderate turbulence 'GPWS/ WIND SHEAR FAIL' was displayed on both Primary Flight Displays (PFDs). Then 'X' displayed on both PFD HSIs in FMS mode.I glanced at the FMS Control Display Unit (CDU) just in time to see it flash a white screen and then go blank. PFDs and Multifunction Flight Displays (MFDs) then blanked. I communicated to ATC that we had a navigation issue; took controls and started to level off the aircraft from climb at approximately 10;000 ft. I requested the First Officer (FO) to advise that we were having nav/ instrument issues.At the time of the failures Autopilot remained engaged. Remainder of flight was made with Autopilot off and on standby instruments. I checked the voltage indicator and it looked normal/ straight up/ above 24V. I selected battery to EMERGENCY to conserve battery power as we were descending in IFR. ATC gave descent to 2;000 ft. and vectors to approach XX .When we were visual and could continue visual to Runway XX I selected battery back to ON. Normal configuration and landing made back to ZZZ. At some point during descent and positioning for approach all displays and FMS returned to displaying information. FMS was initializing. My attention was solely focused on a safe return and landing while flying IFR on STANDBY Instruments. I'm not exactly sure when the FMS and displays returned however I am pretty sure that they returned while the battery was selected to EMER which was confusing and why I recall it as such.Landing ZZZ was approximately 540 pounds overweight