12V battery not charging and P3001

A few months after replacing the Hybrid Battery in my 2001 Prius the warning display came on with code P3011. The car operated fine. Then it started having spells where the engine revved at high rpms. The car would continue to go but appeared to be running only on the high revving ICE. Turning it off and restarting made the problem go away. Some experimentation convinced me that the problem was in the 12v battery although it checked out with a tester. I replaced the 12v battery and the warning display does not come on and the car operates the best it ever has.