Will Prius Prime 12V battery die after a 25 days vacation?

You disconnect the positive terminal using a socket wrench or the like. The positive is the one under the popup cover. Just pinch the cover near where it hinges and it will open easily. Disconnection is your best bet in my opinion. Just remember you may loose your radio presets so write them down. Not sure if you'll loose anything else of importance. J

 

One thing for sure is that keeping the car plugged in with the EVSE will discharge the 12v battery quicker. The EVSE will not charge the 12v battery. For a new battery on your 2021 PP, 25 days may be OK to leave it, but no guarantee. In my experience, leaving the car (not plugged in) but undriven for two weeks caused the resting reading of the voltage to drop below 12.4v from a 12.7v full charged state. My feeling is that if I left for another two weeks, it probably would still have enough juice to start the car. You can take a chance if you have an easy way to jump-start the car if the 12v battery drains too low. But, if you want to play safe so you don't have to purchase a new 12v battery, then disconnecting the 12v battery would be better.

See this thread for more detailed observations of the 12v battery on my previous 2020 PP when it was new but was driven only once a week for ~1hr. 12v Battery Is Discharging, Re-Charge Now ! | Page 13 | PriusChat

 

Ah - highly recommend you disconnect the negative terminal FIRST. If you work on the positive terminal while the negative terminal is still connected you could receive a nasty shock.

 

if you can leave it plugged in, you can put a tender under the hood and close it

 

I think OP meant they can leave it plugged into the high voltage charger, but don't have a household outlet nearby.

25 days is probably OK, but to be safe, you can follow the guidance in the attached service bulletin. Page 4 is about the battery.

 

Just as an FYI - I left my 2018 PP in the garage for 6 weeks (this summer) with no issue. Going to pick up a battery maintainer for the next long trip, though.

* Our Camry battery bit the dust and had to be replaced. It was a about a year from it's expiration date.

 

Grab a 12V Jump starter battery. You can even toss it in the trunk for extended parking at airport lots (avoids needing to chase down a midnight jump after a lonnnng, tiring flight). They come in handy for many other power needs as well.

 

Not really. You cannot get a shock from 12 volts. If you pinch and pull up the red plastic cover on the positive terminal you will see how easy it is. You will need a 10 mm wrench (or socket wrench) to loosen the one nut on the terminal. Slip it up and off and you are fine.

 

Right, not a normal shock risk. But it is a big spark risk, if the wrench swings into grounded metal, which I have witnessed others doing on other equipment. And I hear of cases of the wrench getting weakly spot welded to the grounded item, momentarily delaying efforts to disconnect it.

So disconnecting the grounded side first (negative terminal of almost everything today) is still necessary. Then it isn't really necessary to do the other terminal.

As for 25 days, on a one year old vehicle (and battery?), that certainly hasn't been a problem on plenty of Gen3 non-plugins. So unless a plug-in is worse, ...

But on older batteries, or wounded batteries, it could be a problem. If it is possible to get it close enough to an electric outlet long enough to top it up with a battery tender before the trip, I'd try that as an alternative to disconnection. Or get a jump box.

 

Pull out the D/C CUT fuse #38. This is the fuse in the engine compartment, This fuse is not installed at the factory when the car is shipped to the dealer, It maintains the ECU but does not power the high drain circuits like the Smart Key system.

Toyota Prius (XW50) (2015-2019) Fuse Diagram • FuseCheck.com

 

Interesting. I have never heard this come up for the subject of the 12v battery on Prius Prime. From my experience, turning off the SmartKey function did not prevent the 12v drain. I suspect on Prius Prime, ECU is draining the 12v battery.

 

This! ^^

Not shock. It's only 12V. But burn? You betchya!!! My father-in-law once got his metal watchband between the positive and ground. It was a long time before that burn healed enough for him to wear the watch again. IIRC, the watch survived, but the band didn't.

Remember, it's amps that cause heat and when a car battery puts all the amps it can muster through something that conducts as well as a wrench, things get exciting instantly.

 

It deactivates more than the Smart Key. It cuts off power to all high 12 volt drain systems.

 

I wish I knew about this last year when I had my 2022 PP parked almost 10 mo with only an occasional short drive once a week. If I can, I would try removing the DC/Cut fuse #38 and monitor the 12v battery over the course of a few weeks on my new 2021PP as I did on my 2020 PP. But now, I am driving the car almost every day. I really can't do that experiment. It would be interesting to finding out about others trying this for long-term storage of PP.

 

I’d always notice, in a nearby Honda dealership: all the vehicles in the showroom had the negative cable disconnected.

 

All good advice (and it's disconnect the negative terminal first, always).
One thing Toyota does when shipping cars from Japan is to overinflate the tires to 40 psi to prevent them from getting a hard, flat spot on the bottom while sitting on one spot...I'd do that, too. (Personally, I'd also change the oil before I left and ran it for a while to get that new, clean oil all inside the engine.)

 

OK, I accept the fact that if you tried real hard you might be able to ground your wrench to the body while loosening the nut on the positive connection. Makes me wonder why it is customary to disconnect the positive rather than the negative cable on a negative grounded car. I am also wondering that if you disconnect the 12V battery and close the hood, are your doors now automatically locked? If so, you would have to use the mechanical key, something that I have never tried.

 

I've always heard the opposite: disconnect neg first, or just the neg, if it's just to isolate the battery. It's one of those things I've never understood in-depth, but abide by it.

I have been "surprised" once (with a jump pack battery I was changing): had both cables loosely connected, was wrenching one tighter, and got a big spark and bang, wire fused to wrench. I think the drill is to deal with one cable at a time, neg off first, on last.

How to Disconnect Your Vehicle's Battery

 

Gen 4 I don't know about for sure, but every earlier gen had a cable connection you could just squeeze and unplug, no need to fuss at the battery post clamps with a wrench. For Gen 1 and Gen 2, the cable could be unplugged right at the block clamped onto the positive battery post. For Gen 3, it's a fat white wire plugging into the face of the underhood fuse box. Gen 4 may have something similar; I haven't looked.

In a car with added aftermarket accessories wired in at the battery, those might not be depowered by unplugging this cable.