Yep, same applies with a 4 cell pack.

If you think about 'detecting' a short with a meter before flying, what will the meter show if a cell is shorted?

A shorted cell is the same as simply ripping a cell out of the bat, and replacing it with a wire. So if a cell shorts you've basically got a 3 cell pack (with a bit of extra resistance etc.). Try your setup (and the cross-charge experiment) with one 3 cell pack and one 4 cell pack if you are concerned.