Well, I hate to be in this position! But here goes, I have disconnected batteries with the engine running may times and never seen an issue. Just lucky I guess. And I'm the one that doesn't like people saying "will I never had a problem", LOL. Next time I'm around that situation I'll have to throw a voltmeter on the system.
Here is an interesting video, but it's just something off the internet, so don't mean much. I'll have to do my own testing.
https://www.bing.com/videos/search?q...88E4&FORM=VIRE