A friend of mine had the regular 12 Volt Battery die in her 2017 Prius,.
The Service Manager @ the Toyota Dealer where she bought it, told her under no circumstances try to "jump" start the car.
It had to be towed to the dealer ( covered by AAA)and a New 84 Month " Prius 12 Volt Battery" ( her Warranty didn't cover this) plus reprogramming her Smart Key cost her $389!!!
Sounds excessive to me, does anyone with a Prius have any info on this???
Pure garbage from the dealer! The 12V battery is simply an AGM one that even the AAA will "jump" for you. The difference is, you don't jumpstart the car, you give the battery enough of a charge to turn on the computer which then brings up the 250V battery which starts the car and recharges the 12V battery fully.
I have "jumpstarted" both my hybrids multiple times when they ran down because I left something on (12V battery powers lights, other electrical stuff) and 250V battery said it had to protect itself so it would no longer keep charging a battery that, until the issue was fixed, would keep draining.
I haven't checked the Prius charging but the Camry Hybrid can be encouraged to give the 12V battery enough of a charge from the 250V one in most cases by following a technique described in the manual.
When my 12 y/o Camry 12V battery died in May (had a dead cell), it was 12 years old. The 8/yo Prius is still going strong.
In no case (even when changing the Camry battery) did I have to reprogram the keys.
While the dealers charge a lot of money for their 12V batteries for the hybrids, they are still not cheap. A good AGM battery (I used Optima, considered top of the line) is $150+ and one with a vent tube (needed if battery is in enclosed place like trunk or passenger compartment) is at the high end. AGMs are sealed and can't spill acid but if overcharged, need a vent to avoid exploding. By the way, the charged battery was shipped to me via Priority Mail and was in every imaginable position in shipment, I am sure. It was on its side when dropped off at my front door.
Most times, even when "discharged", the system has enough oomph to keep the critical things alive such as key programming. And if the system is put on a temporary (very small one needed) 12V battery to keep up that life while changing the regular battery out, there should be less of a problem. I didn't bother as I didn't have a battery to plug into the cigarette lighter port (the typical way to keep 12V alive) and had no problem. I didn't even have to "reprogram" the tire pressure monitors. Everything came up fine.
It is really important for hybrid car owners to read their owner's manual closely as the car, having a 250V battery in addition to the 12V one, often has techniques to recover from a "dead" 12V battery or fob battery. More important is to read the forums which have outstanding information about their car even if one never plans to to do the work themselves. I rarely do things myself. However, when I found out in a forum a few years after buying it that my old Camry could be retrofitted with an "intergrated" (in existing NAV system) backup camera, I ordered the camera, downloaded the detailed (with color pictures) 12 page guide to installing it and took it to a local guy who did stereo installs. He said it was the easiest, best guide he'd seen and his charge was a lot less than if he had to start from ground zero.
And when I bought the Camry battery online in May, it came with a detailed instruction including removing and re-attaching both the vent tube as well as the battery temperature sensor which prevents the overcharging issue if the charging system goes wild which was provided by a company that sells only that battery and only for the Camry Hybrid. I installed it myself but could have taken it to my mechanic so he would have known what special things to do - and at a lot lower price than the dealer.