2012 Prius C won't start after changing 12v

I suggest you get the codes read by a code reader that can check the proprietary Prius hybrid codes.

Did you jump start it before replacing the 12V battery? If so, are you absolutely 100% sure you did not reverse the polarity on the jumper cables? If you got them backwards, you might have blown some fuses. Or you might have destroyed some very expensive stuff.

Check the fuses and then read the codes.

 

We get a least one of these a month on Prius Chat... It's almost always because the person bought an Optima Yellow top battery, which isn't really a battery it's a scam sold by a company run buy criminals who re-sells batteries returned as defective because they think recharging defective batteries is all it takes to fix them.

 

I recommend getting a cheap multimeter and bringing it with you when buying a new battery. It happened to me about a month ago that I bought a new battery from Pep Boys and it was reading 12.1v which is unacceptable for a new battery. The second one they gave me read 12.75v which was perfect.

 

We never would have guessed that as the reason. But glad you're back on the road again. Not seating the high voltage safety disconnect is a common oversight when working on the HV system. Pretty rare when replacing the 12V since there's no more reason to pull that orange disconnect than to unplug your refrigerator when working on the 12V battery.