Greeks still exist, and they say bataria (spelled μπαταρία) for an electric battery.
On a more technical/formal registry, the word for accumulator is συσσωρευτής, and another word for battery is συστοιχία. Both words are derivations from roots present in New Testament Greek and would have been easily parsed by any “ancient” Greek, just like an ancient Roman would have recognized the word accumulator without having the faintest clue about what is meant.
While συσσωρευτής is the exact etymological equivalent of accumulator, συστοιχία and battery have somewhat different origins. Battery comes from the old French word batterie, meaning “a set of metal implements meant to be put together to be used” (from artillery to kitchenware: my sources explain the relation with the verb battre, ”to beat”, in different ways and that discussion is off-topic here). Συστοιχία comes from the verb συστοιχέω, “to be tied together one after another”, just as power cells in a battery are: most probably, it was first used of batteries by someone who knew the French etymology.