I have written a book with an ensemble cast. Prior to them meeting, I simply gave each character his/her own chapter. Once they met, I narrowed the perspective to only a couple. The battle at the end, however, needs to have many perspectives. It isn't feasible to give them separate chapters at that point. What is the best way to handle the transitions?
Best way is the way that works... Sadly this is not a simple question to answer, as there would be a host of possible choices.
How does the flow and feel of the rest of the novel fit in with your perspective changes?
What kind of feeling are you aiming to capture with your writing? - If you can come up with an outline of what you need to have going on, and how you want the work to read, then people will be able to give far more effective feedback.
A thought tool that you may find handy:
I like to think through my writing projects somewhat as if I were designing content for a movie - The reader's impression of the work is the camera's view, now how is the camera moving? Is it a tight and close camera that focuses on what's going on with a single character? Does it jump cut to the next character, or is it some kind of a pan?
Is the camera pulled back slightly, showing details across several characters at a time? Maybe the camera is somewhat loose, following one character for awhile before passing off to another without cutting between them as a single shot.
Maybe the camera is pulled far back, like a full on crane or helicopter shot showing the whole battle - Do you need the same narrative tone for your conclusion? What if you had followed the characters closely throughout the book with a first person or close following narrative tone, but now contrast that by 'pulling back' to a more omnipotent narrative voice that covers the entire battle itself instead of being overly tied to an individual? [And unlike a movie, as writers we're not confined by silly things like paying for sets or dealing with physics or post process editing... We have ultimate freedom, assuming we can find the words.]
I have a somewhat similar situation in my piece. It is not a pitched battle, but a firefight that allows for an escape.
I switch between the target of this assault - my MC - his friends guarding him and the task force hunting him. I end up with four main POVs and switch between them when it feels right.
My MC flees with the Secondary Protagonist, the Tertiary Protagonist holds off pursuit, and then there is the Secondary Antagonist who leads the hunt.
The technique I use is, when there is a lull with one, I switch to the other. My main focus is on the pursued, but the others must be there or my MC is fleeing from shadows.
My characters tell me when it is time to shift focus. Later, when I read it aloud to check for flow, I listen to see if the shifts are jarring. If anything is amiss, I add a word or remove a phrase until flow is restored.
We all have our own process. I must recommend the book Bridge Too Far - a fascinating account of the battle or Arnheim and the disasters that occurred. While it is a historical account, it is valuable to show how some perceptions can be rather skewed in battle. For example, one British Major was noted for carrying an umbrella wherever he went - including when he checked the perimeter. Others thought him extremely brave and the perfect example of stiff upper lip. He carried the umbrella because he could not recall the call signs and needed to be recognized by his own men.