I've just gotten a replacement pump from Minimed about 2 weeks ago and did the first battery change last night. After the new battery was installed the pump gave A21 alarm, cleared the date/time and all my CGM graph. Also required me to rewind. It kept all of my settings. I repeated it again and it did the same thing. The alarm history gave A17 and A21. Any ideas?
Yes you need to change our the battery faster to maintain your settings.
Also if you allowed your current battery to drain completey, you will get this alarm.
There is a short term battery in the pump that keeps the settings for 1 min or so after you take out the battery. That could also be failing if you are switching it out fast and it is still happening.