Hello again, Chile79. Thank you for providing very-precise measurements of your huttons' size. I'll add some "more specific" info to what Fyrffytr1 told you. The 15-millimeter size of thin 1-piece stamped-brass 4-hole buttons were most often used as pants-fly closure buttons. Since yours came from a battle site, I should mention, they were used on both Military and Civilian pants. Some were also used on antique long underwear, the type which in the US was called "longjohns" underwear.
One of your 4-hole buttons is marked "Hodgkinson Collier-Y-Cia"... I know a Collier is a coal miner or seller or a ship that carries coal, and the Y is Spanish for "and"... but I don't know what Cia means in Spanish.
The button with script letters EM (or ME) on its front shows the letters encircled by a wreath of Laurel leaves and Oak leaves. Although the buttons of some Civilian organizations and town Police departments show the organization's initials inside a wreath, the combination of laurel and oak leaves is usually a Military-style wreath. Therefore, being found at a battle-site, having that wreath, and the name of a Peruvian button-dealer/clothier indicates the button is probably from a Peruvian military uniform.
