Post jump start Prius
February 10, 2021 5:39 AM   Subscribe

We had to have the 2012 Prius jump started yesterday because it wouldn't start. Probably the battery drained because an internal light was left on. After the jump, the car was left idling in the driveway for over an hour. My question is, what should I do today? Should I wait until the weather gets up to the predicted high of 20 F this afternoon and drive around?

Or should I just wait until the next time I have somewhere to go on Friday, when it's predicted to be about 15 F? Also, any advice about that first drive? Once I had a jump start, in a different car, and made it all the way out to the first stop sign, where I responsibly stopped but the battery conked out again. Most of the neighborhood streets have stop signs, and it is impossible to get out of the neighborhood without stopping and waiting for traffic. Please answer specifically for a hybrid automobile, if you can. I believe they do not have an alternator.
posted by SandiBeech to Travel & Transportation (15 answers total) 1 user marked this as a favorite
Go buy a new 12V battery and replace it.
posted by schwab at 6:04 AM on February 10, 2021 [2 favorites]

A hybrid is a little different than a conventional car with an alternator.

So I have an instructive experience from just a few months back.

Our Highlander Hybrid 2006 suffered a 12V battery failure (as opposed to the traction battery) at the worst possible time; I was on a business trip, in the middle of Nowhere Oregon (sorry Oregonians, you have a beautiful state but sparse dealerships). I was just getting ready to depart, and the car would "light up but not go ready". This is a state where the hybrid system isn't getting enough 12V power to engage. The architecture of the system is such that there is no "alternator" or "starter", so you do not need a strong 12V battery to "crank" the engine. The traction battery does that. However, the 12V system runs all the electronics, including the electronics for the hybrid system. The 12V system is charged by a 100A charging circuit from the traction battery. So, there's a little trick, if you have a low volt 12V battery, sometimes you can get the charging circuit to engage long enough to boost the 12V battery to a point where you can then try to start the car and it will go "ready", at which point you are good to go because the 100A charging circuit will keep things going.

I drove 12+ hours like this until I reached Salt Lake City. Had to keep the car running during fuel fills, because who knows if it would have started again. I was pretty sure I knew what was going on because it's not the first time I've had a flat 12V battery in a hybrid, but it's the first time it happened while thousands of miles from home, and in areas with no cell coverage to call AAA. I went to SLC because it was the nearest city I expected to have a dealership that had experience with hybrids, just in case my guess as to the issue was wrong.

So the thing is, driving around does nothing for you and your Prius. Your Hybrid Synergy Drive is going to be trying to charge the 12V battery, and if the traction battery gets low, your HSD turns on the internal combustion engine and charges the traction battery. None of this is dependent on movement of the car, just on gas in the tank and power in the traction battery.

If the 12V battery isn't failing, an hour of idling is more than sufficient to have given it a pretty good charge, so if you get in and hit the button and it goes "ready", then yay, you might be okay.

Do take a look at your dome light as you do this, if it seems like the dome light is dim, or the HSD doesn't ready in the way you are used to, with lots of warnings and flashing of the lights on the console, then the battery is weak, and will ultimately need replacement.

If your car starts, you do not need to worry about stop signs. It will keep going until you shut it off. Your 12V system is fed by the large charging circuit from the hybrid battery. DO NOT SHUT OFF YOUR CAR anywhere you are not prepared to have it towed from, until you get a feel for what your 12V battery's condition is.

Any car repair, battery store, or dealership can check your battery for you, which is the best course of action. They will need to shut it off to evaluate the battery, but it can easily be started again.
posted by jgreco at 6:10 AM on February 10, 2021 [7 favorites]

Also, if you haven't had the 12V battery replaced yet on your 2012 vehicle, these seem to last 5-7 years in hybrids. You are past due, in my opinion, even if the battery seems to have recovered.
posted by jgreco at 6:20 AM on February 10, 2021 [2 favorites]

Seconding everything jgreco said. If you leave the car on (in “Ready” mode), it will recharge the 12V battery just as effectively as if you drove it around.

And, yes. I left the door open on our 2013 Prius for about an hour back in February 2020 and the battery ran down, which is definitely a sign it needs to be replaced. If yours hasn’t been replaced yet, it’s time. It’s somewhat harder-then-normal to replace the 12V battery in a Prius, so if that’s not something you’re generally comfortable with, you should probably take it to a mechanic to have them do it.
posted by Betelgeuse at 6:56 AM on February 10, 2021

My 12v starting battery got old and unreliable and it was a pain. It's easy to leave a door ajar. Dealers will charge a lot ofr a replacement battery, and so did VIP/O'Reilly. Batteries Plus charged the cost of the battery, easy to schedule. Battery itself was a bit over 200.
posted by theora55 at 7:32 AM on February 10, 2021

Anecdotally, our 2010 Prius battery died in September, and then had to be jumped a few times in the next month. However, since then it has run fine.
posted by Corduroy at 8:56 AM on February 10, 2021

There's also the auxiliary (non-traction, non-starting) battery in the trunk which needs care all of its own.
posted by scruss at 9:25 AM on February 10, 2021

Also - in my experience, once a 12v battery dies and is drained during a cold-weather event, it is essentially toast and will definitely need to be replaced before the next winter - so do it now.
posted by rozcakj at 9:27 AM on February 10, 2021

The 12V (trunk) battery in my 2010 Prius died fairly suddenly 18 months ago. You have to take part of the trunk apart to get to it, but it's a good excuse to vacuum that part of the car out.
posted by dws at 9:27 AM on February 10, 2021

My Prius battery which was 8 years old kept dying on me after we were locked down in March and I wasn't able to go anywhere. In the end, it wouldn't hold a charge and was due for replacement, so I had a new one. The new battery is flat now as I've barely driven, but I'm confident it will either be okay once it's started or, as it's still under warranty, will be replaced. The lesson for me is to make sure I start the car at least every other day, if not daily.

The 12V battery in a Prius is smaller than in a non-hybrid vehicle, so it tends to drain more quickly.
posted by essexjan at 9:35 AM on February 10, 2021

If it's an old battery, replacing it will make a big difference. If you can't do that (or can't do it right away), one of those jump-start battery packs is handy to have, and work just fine on a Prius.
posted by rikschell at 10:22 AM on February 10, 2021

Both our 2006 Prius batteries died at 8 years, and the next set suffered pandemic-related issues this past year when those replacements were 6-7 years old. Replace at 7 or 8 years.

But also, running in the driveway is not very helpful, the engine only cycles on periodically. You will likely need a jump again and then immediately go for an hour drive. Just replace the battery now if it's too old. (Confirmed it is a super-pain to get at the battery compartment in the back, get someone else to do it if you can.)

Strong recommendation to NOT use the lighter-plug jump starters on a Prius, if you like having a working electrical system. You can use a portable jumper that attaches to the terminals (under the hood - the battery is under the hatch but there's terminals up front) or jump from another car. Follow your manual's instructions.
posted by Lyn Never at 11:06 AM on February 10, 2021

The engine cycling on is not what charges the battery in a Prius, and the 12V battery will charge as long as the READY light is lit. There is no need to drive the vehicle around unless you just like driving around.
posted by jgreco at 5:25 PM on February 10, 2021

Response by poster: Thanks all. I made it to my Friday appointment and back with no trouble from the car. I am going to have to spend some time learning about hybrid vehicles.
posted by SandiBeech at 8:50 AM on February 12, 2021

Your car needs fuse call throttle body position sensor. It regulates the contact of spark to the air flow or something like that. The car will act like it's slow to start but really it's not got the right combustion to stay running. This is my suggestion. If the lights are not dim in the car when you start it go there. If they are dim replace the battery.
posted by The_imp_inimpossible at 6:29 AM on February 14, 2021

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