40 below. dead battery - idle to warm questions

It's between -35 and -40 F. (Have used '07 Prius, 30 K miles & no manual except the small pamphlet)
1. Plugged it in 2 hours. Started & idled for 20 min while scraping windshield & running defrosters.
2. Drove to have new tires put on in a shop and then it was dead in the garage bay. They jump started the 12 volt under the fuse box in front. 3. Drove again & parked, plugged in. Three hours later, totally dead.
4. Dealer swamped - says jump it and leave it to freeze outside at the dealership & they may get to it in a week.
Question: Is the battery under the hood the famous 12 volt? If so, what is the battery in the rear of the car that I've heard of. I guess they will take out that front battery, test, tighten connections, etc. and either say it is fine, put it on a charger, or sell me a new battery. Are these reasonable assumptions on my part?
Question: what do you think happened? Did I do something wrong as stated above at the beginning of this post?

Yes, it is the original battery. Yes, they may have left the hatch open indoors (where it is warm) while dealing with the tire change out. Do 12 volt batteries have a shelf life?
(and yes, it was -54 in Fort Yukon), but a far cry from the minus 60s we used to enjoy here)

You've got my attention. HOW do you deal with sub -34F up there as far as coolant goes? Doesn't the pink Super Long Life turn to slush after cold soaking at those temperatures? Is the block heater sufficient to keep this from happening? It is something that I have wondered about, how you folks deal with supercold temps when the factory 50/50 premix only protects to -34F. Do people run 70/30 in Toyota red (Long Life) instead?

I think your battery is completely dead and beyond recovery.

While the new pencil post Optima DS46B24R is all the rage, you might be better off cost-wise getting the old D51 kit from elearnaid.com, since they ship via Priority Mail.

From my understanding (but based on a single -41F event, and asking around among the local automotive types at that time), slush still works.

BTW, this was not in a Prius, but in a previous era.

My '04's 12v battery (yes, it is in the trunk on the right side, just below the deck, too) died a few years ago, too. I couldn't figure out why, but bought a new spiral-wound model for a monstrous price and installed it myself. It also went dead once or twice, but a trickle-charge brought it back and it's been fine for the last year or two.

I'd suggest putting a trickle charger on the 12v connections under the hood or rigging some kind of fused connector under the hatch so you can plug it in easily.

The light under the hatch can be turned off, but if opening the hatch lights all of the interior lamps, that won't make much difference.

Sounds like your battery just hit a normal end of life, which, in my experience, is within a few minutes of when the warranty runs out.

Oh, and by the way, the 12v battery just "boots up" all of the computer systems in the car; it doesn't start the engine, and that's why it's not a huge battery and why it can be located so far from the engine. One of the motor-generators in the powerplant under the hood acts as a starter AND generator and runs off the high voltage propulsion battery behind the back seat.

hope that helps... happy motoring, even if you're freezing your butt off in winter!

How cold is the main traction battery? The small 12v battery just starts the electronics, but the main battery actually spins up the gas engine to start the car. Maybe it's too cold to work?

I just can't resist:



+1 on replacing the OEM 12V battery.

Although it won't help with overnight cold soak, recommend full grill
blocking to retain heat once underway

I'd say that 4 years is a reasonable life expectancy for the little 12-v. battery. The extreme cold just makes it worse. If the battery is not the cause of your problems, it will soon cause problems, given the age and the weather. I'd suggest replacing the 12-v. battery. It will either solve the problem, or prevent problems when it gets REALLY cold up there.

Methinks that the inverter cooling pump would bite it, being the fragile little thing that it is, if trying to move slush. Not that you need any sort of inverter/trans cooling when it is that cold, probably would not even notice until late Spring. Sigh...the experimentalist in me is always curious but glad to live in the comparative warmth and sunshine of Santa Fe, a balmy +34F right now.

Brrr.....

It's making me feel cold just reading about those temperatures OP is experiencing. It was 95F (35C) here yesterday.

Actually a few miss-conceptions here.
First, the coolant doesn't turn to "slush", it just thickens a bit. It's good to -40 as I recall and probably will be fine even below that.

Second, while starter lead-acid batteries have serious problems -delivering- power at -40 it doesn't actually hurt them unless they freeze and crack the case. Prius 12 volt batteries in cold places, in my experience, seem to last longer than in hot places. I think this is because the primary reason for failure is loss of water (ignoring repeated full discharge).

I do expect you need a new 12V battery. You can get a stock one from the dealer or an Optima. I like the way e-Learnaid does business within the US, with rapid delivery of good product. Unfortunately it's rather expensive to ship here in Canada, but I digress.

To get to the 12V battery, remove the hatch floor, remove the cargo container, then remove the small "floor piece" on the right hand side. All without tools. You can now see the 12V battery, surrounded by "other stuff". If you are going to change it yourself remove the negative lead first and replace it last.
You will have to re-set the auto window down and all your radio presets. You may have to press "start" twice to clear the "cobwebs" from the computers. It's not a big deal.

When the temps drop below -10 your car should be plugged in at all times when not in use! Would not hurt to have a heater in the car to help keep the 12v warm! I would be using 0-20 oil as well. Hal

If the water molecules form ice crystals at -34F in a 50/50 mix, then that acts to decrease the water concentration in the liquid that is left behind, and lower the melting point, which bottoms out at -67F with a 70/30 ratio of glycol to water. I could see pink SLLC going from soupy to slushy to frozen as the temp falls below -34F

Ha, love the joke & printed it off for all those here who relate to that cartoon.
I will let y'all know on this thread when we arrive at the solution. Thank you one and all for actually thinking about it and taking the time to sit down to compose an answer to my query.
Cloud cover today with much warmer temperatures. Cold then returning, but hey, that's what we like up here. Winter. Where else can you run to town and see skiers along the bike paths and a team of dogs whizzing along pulling a sled and driver? Mid morning and early afternoon pastel sunrise/sunset? Hoar frost. Nice.

I drove the Prius for one and a half winters in Fargo, North Dakota. I didn't have a block heater, so the car was never plugged in. I never had any trouble with it. However, during that time I never saw it get colder than 30 degrees below zero Fahrenheit.

A block heater would probably improve FE, but the car is fine without it. Inland Alaska is another matter. That's outside my experience.

I once saw a team of dogs pulling a sled and driver (musher?) running parallel to I-29 a short ways north of Fargo, North Dakota.

Aspens3, were you plugging in a block heater, or a trickle charger? In any case as others wrote the old 12V battery is now dead.

Buy the correct year owner's manual from a dealer or online. It's full of info that you need to know.