Just out of curiosity...how absolutely necessary is it to disconnect the battery before swapping the RCM?

The reason I ask is a few nights ago I had the no-start issue while leaving a resturant. I'm 95% certain it's the RCM, plus I've been having occasional P0410 triggers anyway. I carry a brand new MB spare with me but I did not have the right socket for the battery terminal. While checking everything and deciding if I would try to swap it without a battery disconnect my Crossfire decided to start and drove home just fine.

I got home and made the swap. I'll work on shipping the old one to tighed1 next week.