Ok, so a few days ago when I got off from work my 2010 Prius wouldn't start. It made this little humming noise, but the display lights wouldn't come on. I got out of the car, locked the car, and after a few minutes got back in the car and it started just fine. I ran an errand that evening and it did the same thing. I took it to the dealership the next day, but their hybrid specialist wasn't there. They still checked my auxilary battery and ran some sort of diagnostic to check for codes. He said he couldn't find anything wrong with my car. So it worked just fine for the next two days. Then this morning it wouldn't turn on at all, no orange light, no display lights...nothing, not even the whirring sound. On a hunch, I went and got my spare key. I was able to start the car with my spare key, but when I got to work I couldn't lock my car with my spare key. I had to use my original key for that. (My car is completely keyless.) I had the batteries in both of my keys replaced about a year ago, and I haven't seen the "key battery low" display recently. Any ideas?
welcome! dealerships frequently misdiagnose the 12 volt battery, and they are notorious on the 2010's. i would either do some more testing, or just replace it. you can also check the battery neg cable to body connection and all the connections while you're in there. all the best!
+1 on 12v battery, if the battery is marginal at all replace! Most auto parts houses will check for free.
2010 was the first year of the Gen III, so it's not surprising that there are gremlins in that year's cars. I notice that a number of our best posters often advise a battery replacement, but often it's something more modest.