1530s, "action of battering," in law, "the unlawful beating of another," from French batterie, from Old French baterie "beating, thrashing, assault" (12c.), from batre "to beat," from Latin battuere (see batter (v.)).
Meaning shifted in French from "bombardment" ("heavy blows" upon city walls or fortresses) to "unit of artillery" (a sense recorded in English from 1550s). Extension to "electrical cell" (1748, first used by Ben Franklin) is perhaps from the artillery sense via notion of "discharges" of electricity. In Middle English, bateri meant only "forged metal ware." In obsolete baseball jargon battery was the word for "pitcher and catcher" considered as a unit (1867, originally only the pitcher).
c. 1300, doseine, "collection of twelve things or units," from Old French dozaine "a dozen, a number of twelve" in various usages, from doze (12c.) "twelve," from Latin duodecim "twelve," from duo "two" (from PIE root *dwo- "two") + decem "ten" (from PIE root *dekm- "ten"). The Old French fem. suffix -aine is characteristically added to cardinals to form collectives in a precise sense ("exactly 12," not "about 12").
The Latin word's descendants are widespread: Spanish docena, Dutch dozijn, German dutzend, Danish dusin, Russian duizhina, etc. The dozens "invective contest" (1928) originated in slave culture, the custom is probably African, the word probably from bulldoze (q.v.) in its original sense of "a whipping, a thrashing."