My 12V Battery is dying

That's kinda normal for my gen4 (11.85V); it still starts and I believe that it will continue to do so down to about <10.5V. I've notice that it's pretty cold there; the snowflake symbol in your dash. Battery may be fine, just cold.
Whenever I find my battery that low, I put it on a 6A charger for an hour or two - then it's fine for another 6 months. It's been worse since I retired and the car is no longer a daily driver.

Walmart has a 140R AGM battery currently on-sale (flash sale) for around $106.

Good Luck...

 

You're way outside of warranty for the battery. Time for a new one.

As for driving it like that, chances are you'd get stranded in a parking lot because it's only going to get colder. Cold kills a battery fast, even if it inside the cabin.

 

Where do you live?

My (limited) understanding is that warmer temperatures tend to cause the car to not charge the battery as much, and thereby causing premature failure. I usually get 4 years on a 'normal' car battery.

I bought a BM-2 battery monitor the other day, and it's a fun toy. In the winter here so far, charging voltage on my new-ish LE hasn't gone below 14.4 V. I'm assuming in the summer if it shows that it's dropping, I'll put a battery maintainer on it once in a while to hopefully extend its life.

I think the main dips are for the EVAP pump (if my terminology is correct).

 

Yep, looks like you dipped below the 12V threshold in 12/12 and 12/13; about where the OP is. Your correct, the EVAP & ABS pumps draws a lot of current for their tests.

 

You've piled on the miles pretty quickly, are there any times the car just sits, say2 weeks at an airport?

What's your parking situation? Do you have a secure garage with AC outlets, or?

 

Well if the dealership says: 'there's nothing wrong with it' - I pickup a cheap jump pack, while they're still on-sale.
That'll ensure that you won't get stranded for a dead battery. They're going for about a third of the price of a new battery.
Beware; those lithium jump packs don't like the cold either - you may have to warm them up in your jacket; if you keep it under the seat of your car. Your better off placing it in your backpack or brief case and taking it inside with you - so it works anytime you need it.

Good Luck.....

 

yes, jump pack, even if you get a new battery

 

For the Prius, and hybrids/EVs in general, cold cranking amps aren't important. Reserve charge is. Reserve charge is how long a battery can supply power at a given draw before it drops to 10.5 volts. The higher a reserve charge in minutes is, the better.

 

Looking again at my chart, I can tell that shorter trips tend to not bring it up to as high of voltage as longer trips. So, after a while, the little trips could take a toll on voltage.

 

Yep; those short hop deficits add up and can kill your battery; without the battery maintainer.
Your chart clearly shows a slow decline, until the 13th-14th - I'm assuming that's when you plugged in your battery maintainer?

 

No. I took a longer drive.

 

If you don't mind; how long was the drive? How many minutes/hours and distance did you travel to achieve this?
And is that battery voltage sensor connected or disconnected?

 

If we've got pending short-run chores, we'll try to let them slide till we're going to be doing a good drive, then do them all in the same day. And keep the battery on a maintainer in between. It helps immensely, being retired, and having a garage with AC outlets.

 

drive to the furthest place to warm the engine, then work your way back

 

If possible. A common scenario for us is an evening run out to the airport (across town) to pick someone up, we'll do chores in the afternoon, walk the dog, have dinner, then do the long drive to airport. Not ideal, but not bad either.

 

. I thought we would be one of the lucky ones and avoid the 12v battery problem but not so. We have a 2024 Prime XSE (18000 miles), driven daily and charged routinely overnight. Yesterday my wife parked in a parking garage for a few hours while at an appointment and couldn't start the hybrid system, just got flashing lights on the dash, and then eventually nothing.. Nothing electrical would operate including door and rear hatch latches. Fortunately AAA responded with a jump pack and knew how to access the jump location in the underhood fuse box. That worked and I started the car and used the charge mode while driving it to the closest dealer. ICE engine ran but sounded rougher than usual. I don't like that dealership but numerous warning lights and messages were displayed so didn't want to drive it very far. Service manager messaged me this morning and said the battery was dead and would be replaced. He got a little irritated (ALL CAPS TEXT MESSAGE REPLY) when I asked if they would please check if the T-SB-0054-24 bulletin applied regarding sleep mode with the charging cable attached.
While waiting for AAA to show up in the parking garage I tried to open the rear hatch manually from the lever inside the small access door on the rear hatch but couldn't budge it. Any tricks to doing that just in case I need to access the 12v battery (open the hatch) with no power on the car?

KH