I can understand where the terms 'pit' and 'front ensemble' come from, but in my research, I can't seem to figure where (or when) the term 'Battery' got its definition.

Any suggestions?

Thanks in advance!

To batter means to hit.

The times where I've seen it in in orchestral repertoire, it's been "batteria" or batterie and the parts have been the percussion "battery" - snare drum, tenor drum or field drum, bass and cymbals. Those are spellings from European languages, so (assuming marching drums came from the fife and drum groups of our military history, which I don't know to be true) I'd say "battery" came overseas from the European classification of the basic unpitched percussion.

I don't know where the use of the word in percussion began, but it's a pretty widespread percussion term and predates modern American-style marching percussion.

In some languages, the word "battery" is used for a set of drums

Language: drum, drum set
French: tambour, batterie
Italian: tamburo, batteria
Spanish: tambor, bateria

In Brazil, the marching drums in a samba performance are collectively referred to as the bateria.

It comes from the term batterie which has had it's meaning stated above. I still refer to it as batterie percussion and I have seen the word used by other people as well.