# Prius battery , confused.



## Nik333 (Mar 1, 2015)

Why don't you just call your Roadside Assistance. They should be more expert and you can watch them. Parts are so expensive, I wouldn't want to DIY it the first time.

You know there are two batteries, right?


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## papereater (Sep 16, 2016)

Nik333 said:


> Why don't you just call your Roadside Assistance. They should be more expert and you can watch them. Parts are so expensive, I wouldn't want to DIY it the first time.
> 
> You know there are two batteries, right?


No, didnt know! Guess thats part of my edjukayshun on prius's. Theres one batt at front drivers side. Wheres the other? I DIY much auto work, nik. not afraid of a batt challenge. Just gotta learn. From people like you!


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## papereater (Sep 16, 2016)

Who knows, maybe its still under the typical 3 yr warranty. Replace for free. We'll see.......


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## Nik333 (Mar 1, 2015)

I'm a newb. This is a good site in my new opinion. Beware of advice from people who don't know the hybrids. Even the Mitsubishi Auto Dealership in town is hesitant to work on Priuses.









Charging the 12 Volt Battery


We have a 2007 Prius and a 2015 Prius. I recently installed new 12 volt batteries in each. I wasn’t sure that these batteries were fully charged...




priuschat.com





The big one might cost you $2000. Using Occam's Razor's thought, that the simplest answer is usually the correct one, I'd assume the little battery is the problem.


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## Nik333 (Mar 1, 2015)

Are you sure you have gas?😈
My Prius even stumped 2 CHP when out of gas.
They don't like significant weather change. The car that is, the CHP, I don't know what their preferences are.


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## Unassailable (Aug 14, 2021)

The regular battery is in the trunk, rather than under the hood of a regular car. Mine lasted 7 years so not sure what's up with yours. Maybe you left the lights on. Do to the cost of the regular 12v battery, I just installed an optima.


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## rogerwh (Mar 1, 2021)

I have a snowbird friend and his 2012 Prius wouldn't start when he returned home from Arizona. We just hooked the charger up to the battery, under the hood. Battery under the hood is the starting battery. It took enough charge, in about two hours, to start the car.
I believe he found charging instructions in his manual.


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## Unassailable (Aug 14, 2021)

rogerwh said:


> I have a snowbird friend and his 2012 Prius wouldn't start when he returned home from Arizona. We just hooked the charger up to the battery, under the hood. Battery under the hood is the starting battery. It took enough charge, in about two hours, to start the car.
> I believe he found charging instructions in his manual.


Which Prius? 12v starting is in the trunk.


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## rogerwh (Mar 1, 2021)

Unassailable said:


> Which Prius? 12v starting is in the trunk.


I was talking about a 2012 Prius, how bout you?

Here is a pic of a 2017 Prius Prime.


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## Unassailable (Aug 14, 2021)

rogerwh said:


> I was talking about a 2012 Prius, how bout you?
> 
> Here is a pic of a 2017 Prius Prime.
> View attachment 669749


I am also talking about a 2012. We've owned ours since new. That's why I asked. I haven't known any gen 2 that had their battery in the engine bay. I could be wrong. That's why I was asking - so which model was it? Looks like there was the switch in 2016.

Regardless of location, as mentioned before, the Prius has a separate starting battery that a lot of people only think the hybrid battery controls all electronics, which is not the case. If there was any issue due to the hybrid system, it would throw codes which you could figure out from the owners manual.


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## raylo32 (Nov 25, 2006)

I always wondered why Toyota included a separate starting battery and not just have a 12v tap from the hybrid motor battery. I suppose the idea might be that you could start and run the car even if the hybrid battery was dead but it is hard to imagine that it ever would be so dead that it couldn't start that teeny gas engine. And being that they have the separate starting battery why didn't they enable it to at least be able to start off the hybrid battery if and when the 12v starting battery is dead?




Unassailable said:


> Regardless of location, as mentioned before, the Prius has a separate starting battery that a lot of people only think the hybrid battery controls all electronics, which is not the case.


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## lenaitch (Feb 10, 2014)

raylo32 said:


> I always wondered why Toyota included a separate starting battery and not just have a 12v tap from the hybrid motor battery. I suppose the idea might be that you could start and run the car even if the hybrid battery was dead but it is hard to imagine that it ever would be so dead that it couldn't start that teeny gas engine. And being that they have the separate starting battery why didn't they enable it to at least be able to start off the hybrid battery if and when the 12v starting battery is dead?


There was a really good link on another thread (I 'think' on this forum) that explained why they use a separate 12v system w/battery, primarily for electrical safety reasons. It seems the 'big battery' has a number of shut down protocols.


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## quatsch (Feb 4, 2021)

I thought "starter battery" (12v) & "traction battery" (many volts, many A-h) but our vehicles use only Gasoline.


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## papereater (Sep 16, 2016)

OK, people, you heard Nik, lets be careful here. A little knowledge can be dangerous........(joking).


Nik333 said:


> Are you sure you have gas?😈
> My Prius even stumped 2 CHP when out of gas.
> They don't like significant weather change. The car that is, the CHP, I don't know what their preferences are.


Got gas. Car sat for 3 weeks though. Whats CHP? Cheap Horse Power?


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## papereater (Sep 16, 2016)

Its a 2017 or 2018, not sure at this point. But I now learned there is a 12v batt in trunk. Let's see.......


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## Nik333 (Mar 1, 2015)

papereater said:


> OK, people, you heard Nik, lets be careful here. A little knowledge can be dangerous........(joking).
> 
> 
> Got gas. Car sat for 3 weeks though. Whats CHP? Cheap Horse Power?


California Highway Patrol.😄


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## papereater (Sep 16, 2016)

rogerwh said:


> I was talking about a 2012 Prius, how bout you?
> 
> Here is a pic of a 2017 Prius Prime.
> View attachment 669749


Yes, my car looks like that. Batt in front left side.


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## papereater (Sep 16, 2016)

The good thing is I have time to fix this- about a month. (still working on my 87 sunbird clutch).


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## raylo32 (Nov 25, 2006)

Yes, but the main drive battery is many cells and it would be easy to tap 12v off three 4v cells. Or better yet just use one of those step down converters like we talked about in the other thread to create a 12v source. If not in place of the starter battery than as an option if and when the starter battery is kaput. But I get what Lenaitch is saying, there may be some concerns with having the main battery interfacing with the gas engine and car's 12v system. The starting part would be easy but having it float like the starter battery does would be more complicated. 




quatsch said:


> I thought "starter battery" (12v) & "traction battery" (many volts, many A-h) but our vehicles use only Gasoline.


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## Unassailable (Aug 14, 2021)

Not sure if you got this resolved. But yes it does look like you are 12 volt starting battery is in the engine bay. So should be easy enough to take to local auto parts store and have it tested.


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## papereater (Sep 16, 2016)

Unassailable said:


> Not sure if you got this resolved. But yes it does look like you are 12 volt starting battery is in the engine bay. So should be easy enough to take to local auto parts store and have it tested.


Thanks. So far, even with all the advice/opinions, this seems to be a bit confusing, so I will try to do the easy 1st, like you said, then see where it goes. A 4.5v battery has got to be bad news. I think that battery is original from the dealer so, 3-4 years on it.


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## ukrkoz (Dec 31, 2010)

Prius Prime? Isn't that the wall outlet chargeable one? 
Anyhow.
So they moved battery from the trunk to the engine compartment on Primes..
OK, Toyota hybrids have 2 batteries. One is power back up 12V battery and one is traction, aka hybrid battery, under the rear seat.
Anything below 11.7V on 12V is considered low.
Yes, battery can be charged just like any other battery except that OEM battery is deep cycle, so deep cycle capable charger should be used.
Recommended is charging either off the (+) bus in the fuse box and any known (-) on the engine or, maybe they added charging bus on the (+) clamp now. 
Try to avoid removing 12V by all means, they don't like that. Hybrids.
There are multiple replacement options. 








12v ALTERNATIVE


Credit goes to a CD poster howardc64 Looks like group 24 batteries are a perfect fit. Got one from Pep Boys (Bosch AGM 24) that measured 10" x 6.5" x 8" so identical to the Panasonic. The +- posts are in the exact same location as the Panasonic (group 24F (I guess F=flipped?) has the +-...




www.toyotanation.com





As ECU and other key electronics run off 12V, car will NOT system start, if 12V is low.
12V is charged off traction battery via inverter, when vehicle is in motion. 
Traction battery is safeguarded as the crucial system components and, will not discharge itself to charge 12V.
So if you stow vehicle for about a month, have trickle charger on 12V.

Otherwise, for those, who stow vehicles in their summer houses or else, it needs to be 
1. parked with traction battery fully charged
2. 12V fully charged and with charger on
3. driven every about 1.5 month, so that traction battery recharges. 
It needs babysitter, in plane words.








Hybrid Long term storage


Has anyone stored their hybrid for a long period like 5 or 6 months? I didn't think it was possible without running the traction battery down, but a neighbor says she has done it twice with no problems. If anybody has done it, any special things done? Bob I have a 2008 Prius, live in Florida...




www.toyotanation.com












Prius 4th Gen - Hybrid (2016-2022)


Toyota Prius Hybrid discussion for years 2016-2022




www.toyotanation.com


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## quatsch (Feb 4, 2021)

Lead acid SOC
full 12.6
half 12.3
empty 11.7


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## Brainbucket (Mar 30, 2015)

Be careful. I don't know bout Prius but the orange jacked wires are either 330 or 660 volts and will kill you. Pulling the 12 v battery should be ok. I've done a few. Disconnect negative first and connect last.


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## papereater (Sep 16, 2016)

OK. Good to know. UK, your post is for upper level mechanics. Im an old style DIY guy. Old style, no elec car astrophysics. Thats my problem. I will heed the warnings from Brain about the high V orange wires, and go from there. But UK, I appreciate your education. Will find out if it is prius prime. Its not my car, a friends.


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## ukrkoz (Dec 31, 2010)

Not really.
It is very simple.
Wheels charge traction battery, when car rolls with inertia. Surplus of that energy charges 12V. That's it. 
You do NOT go anywhere close traction battery, if what I said is Chinese. 
You have dead 12V that needs to be charged with deep cycle capable charger. It should say right on the charger - Deep Cycle (capable).


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