Today after drove around town and then stop to pick up lunch, my 16 prius displayed 12V voltage low and not able to start. after a few tries, the 12v battery went complete dead. After I jumped start the prius, I can drive but there are "hybrid system malfunction" and "low brake power" messages popped up. Would replace the 12V battery cure this?
First thing I'd do is take the 12V to a battery shop and see if it can be revived (brought back to life). Don't jump to the conclusion the battery is "dead" and needs to be replaced. That's a lot of money on a hunch. See if it can be re-habilitated first.
Contrary to "marketing hype" from charger makers, once a lead acid battery is "worn out", it can NOT be recovered. Now.....if it is simply low on charge and hasn't been left sitting that way too long, it might just need a recharge. Might. Also not mentioned yet in this thread......it also could be a loose or corroded connection at one of the 4 "main" battery cable connection points.