I would think you'd have made eye contact and sussed each other up for some time, and the battle cry is something that breaks tension and releases.
But you know...the term in Japanese might have other connotations that you could support by finding contemporary writings...maybe there is hope for my fart joke interpretation yet...
I think in this doka, "battle cry" is kiai. What is kiai? A sudden expression of energy. For me, this is an indication that the proper training solicits a postures that creates the potential to express energy. I am moving away from "release" because releasing energy necessarily creates a need to restore energy. I am more a fan of the concept of energy through balance - a constant state of potential/kinetic energy that never has "down-time." If you kiai in the woods and no one is there to hear it, does it make a sound? Yep.
Also, I think we need a differentiation between a kiai and yelling (which is not an expression of energy) and the possibility that the sound is only a metric of success of kiai because you can kiai without noise. In other doka, sometimes O Sensei talks about opposing sounds (Yah and Toh, for example), I think as a cycle of energy. The "sound" is simply a guide to the posture and movement (for example, "Toh" is sometimes explained as exhalation). We often see tori fune taught with some vocal component, presumably to help create the proper exercise movement. Otherwise, it's just yelling.