Question on Batteries, ESCs and BECs

My winter project is an E-flite T-34 Mentor electric. I like scale/warbirds and this is a low wing plane that can transition from a trainer to a sport, performance wise. The plane comes with a 40 Amp Electronic Speed Controller (ESC) and E-flite power 25 890 Kv motor which supposedly gives good performance but even the manual suggests eventually upgrading those components. The manual also indicates that even with this setup, I can go from the supplied 3 S 11.1 volt battery, to a 4 S 14.8 volt battery.

This leads to my question. The ESC has a battery elimination circuit (BEC) but I've read it’s impossible to use a BEC with anything over a 3 S battery. (My present Castle 60 Amp ESC with BEC even warned me to use a separate battery and cut the power wire going to the receiver for anything over a 3 cell battery). If I go from a 3 S to a 4 S battery, will the BEC fail? How about in general? Are there ESC/BEC combinations that work with larger (5 S or 6 S) batteries or should I always count on adding an additional battery for the servos and such? I know I can purchase a separate BEC but if I can go with an ESC with one built in, it makes more sense and costs less.

Paul L.