I wonder whether this is
a terrible pun on The Charge of the Light Brigade, as immortalized by Tennyson's poem.
If so then
"we" are the British light cavalry who on 1854-10-25 made an ill-fated attack on the Russian artillery, and according to Tennyson the number is 600. (The actual number of deaths was quite a lot less than that. I don't know exactly how many soldiers were really involved.)
Our polarity was mentioned but never revealed
That is, our charge. It's even in the title! But Tennyson inexplicably neglects to say whether it was a positive or a negative charge.
Coulombs we made, but our fate was sealed
Once again, they made a charge. But "all the world knew / Someone had blundered", and they were doomed to "do and die".
Repelling the dark, we refused to yield
They were of course the Light brigade. "Boldly they rode and well, / Into the jaws of Death, / Into the mouth of Hell."
They had a battery: We died in the field
Quite a considerable battery. Cannons to the left of them, cannons to the right of them. Tennyson even uses the word: "Plunged in the battery-smoke / Right thro' the line they broke". But, alas, many of them died. It was, of course, not actually an electric field.