The 35V 22uF CAP is I believe the original part list in design. The maximum voltage that is called for in this part of circuit is 33V. CAPs should be sized at 1.4 times the maximum voltage exposure. 50V 22uF CAP would be preferred, but the 35V will work just as well. I have selected that 35V in my build for the physical size of the part only. If you have more room on your circuit board then you can easily place larger cap there.
This part of circuit is not critical for device operation. It drives the LED indicating light that tells you that batteries only supply 17 volts after which the LED will stop blinking.