I believe the MC90 is actually a Maksutov Cassegrain and not a Schmidt Cassegrain optical system.

True that you have to tell the computer where and when you are but really - how hard is that? As for the batteries - I have used the external jack and an older Celestron Power Tank. Yes, AA cells can be used but I have no experience with that approach. The scope will run just fine with the external power. The mount speed selection is a true PITA and the finder scope is best replaced with a red dot. I found that a wrap of pipe tape on the threads of the altitude lock made it much more secure.

I have the 70/400 refractor and if your MC90 is as good, you whould be pleased.