An SR22 pilot experienced an altitude deviation when he was distracted by weather and an alternator failure.

Narrative

I had an alternator failure; the second one in 6 flight hours; and was diverting. I was above the cloud deck at 12;000; with cloud cover being approx 50%. ATC told me to descend to 11;000. As I recalled at the time I believed the descent was to 10;000 FT so set the autopilot to 10k. Apparently I confirmed 11;000 according to ATC; but then I programmed the wrong altitude of 10;000. ATC called when I was at 10;300 and indicated 11;000 was the assigned altitude; which I climbed back up to. At the time I was in VMC and there was no other aircraft nearby. A compounding distraction was there was a cloud deck ahead that I expected would contain ice as I had picked up some flash ice just prior to the alternator failure. Just after the discussion about my incorrect altitude I requested lower and the controller gave me 5;000. To prevent this from happening again; I've started to set the altitude preselect first and then verbally confirm from that reading; rather than confirm and then later set the altitude. I do this procedure when changing frequencies; set; then confirm and that works well; other than in very busy airspace where an immediate response is appropriate.