I use the Minimed Paradigm 515, and the AAA battery lasts about a month. I keep it in “vibrate” mode (which uses more battery power than the beeps), and use the backlight frequently at night.
MM says the pump is optimized for Energizer batteries, and strongly suggests to only use Energizers. I thought that was just a gimmick/marketing ploy, but for some reason it holds true. When I tried Duracell batteries, they only lasted a week! I think this has to do more with the way the pump “measures” the remaining battery life as opposed to the actual life of the battery, but I didn’t take my experiment that far. So stick with Energizer for Minimed.
Rechargeable batteries have a different chemical composition than regular alkaline batteries, so the voltage they produce is slightly less than a traditional battery. I wouldn’t advise them. I buy a large pack of regular batteries at Home Depot (or even larger at Sam’s Club) and then I don’t have to worry about running out for about a year. I also keep one spare battery tucked in the pouch of my meter’s case, just in case I need it when I’m away from home.
It’s really no big deal at all to change it. Just pop the old one out, and the new one in. I don’t need to worry about losing any information stored in the pump at all.
I should also add that I change the battery when I have one (out of four) bar left on the battery-strength meter. My CDE, by the way (who’s also a Type 1 pumper) changes hers when it goes from 4 to 3 bars, but she admits to being a little paranoid! So “how long does it last” is a bit of a loaded question. Some might be overly cautious, and others might wait for the flashing, beeping “LOW BATTERY!” alarm.