Battery keeps dying overnight, already replaced once

When a fairly new battery keeps going flat, the usual suspects are a parasitic drain (something staying awake after the car is off), a charging system that is not fully recharging the battery, or a battery that was damaged by being run flat.

On modern vehicles, common drains include aftermarket devices plugged into power outlets or the diagnostic port, a dash camera, a door or liftgate switch that makes the car think a door is open, or a module that does not go to sleep.

A shop can do three quick checks: test the battery itself, test the alternator output while running, and measure the current draw with the car locked and asleep. Comparing that draw to normal values usually narrows it down, and pulling fuses one at a time can find the circuit. We would start there before replacing another battery.