My First Alert Smoke Detector/Carbon Monoxide Protectors were eating batteries every 3 months. They were one year old when this started. I used the Duracell Red Batteries, not cheap and the date was good and they were fresh because they are working in everything else.
I called First Alert and they graciously sent out units that last ten years before they need replacement. No more beeping at 2 AM. No more batteries no more ladders crying only one person at a time, please!
The new Detectors fit in the old holders on the wall.
Pay for the best you can find because you're betting your life on it.