Anyone else having 12V battery issues?

Hi Okinawa - I see that your car is not a PIP. You are wise to follow the advice of mindmachine. Those of us who have a PIP, keep in mind that the 12v battery charges from the traction battery. If the car is in READY, the traction battery is open for action and will charge the 12v battery if needed and if the traction battery needs charge, the ICE will come on. The other point is that when ever the traction battery is charging, the 12v battery is charging as well.

With the PIP, 12v battery problems should be rare and will likely be on account that something needs repair or that doors and trunks need to be closed tight. If the door or trunk will not lock, it is not closed tight enough.

 

Not disagreeing, but why did Toyota put the remote A/C capability on an app, given this. My understanding is the remote start of the A/C does not allow the ICE to run.

 

I think that you're saying that you believe the A/C runs from the 12 volt battery? It doesn't. It runs from the main traction battery pack. I don't know if the DC/DC converter runs with the remote A/C, though. Does anyone?

 

OK, did a quick experiment. It looks like Remote Climate (activated by keyfob or the app) puts the car in IG-ON mode. I recall with the Gen 2 Prius it was suggested that this is not a great mode as it ate up the 12v battery and (IIRC) there's no connection to the traction battery in this mode. But you're right, without the traction battery supplying current to the A/C compressor, it wouldn't make a lick of sense.

Maybe one of the more technical folks can answer this in depth, but my thinking is the limitation of 10 minutes for the remote climate is to protect against any excessive battery drain.

 

Call me hard to please, but I find it a major inconvenience that the Prius auxiliary battery seems to go dead so quickly. I'm no electronics engineer, but it seems like rudimentary engineering to have some sort of regulated bridge between the massive 4.4 kWh traction battery and the puny auxiliary battery, so that the large battery can charge the auxiliary whenever it gets too low. I've had to boost the aux battery twice now since I bought the car less than 3 weeks ago, and I've done nothing I'm not accustomed to doing with any of my previous vehicles; listening to the audio or programming the GPS on acc power for 10-20 mins at a time.

 

How inconvenience is it to press brake and power button to put vehicle is READY mode where the large traction battery gets connected to the vehicle power circuits and the ICE will run as needed?

Also found this old Toyota document here on PC; http://www.toyotaegypt.com.eg/images/phv_overview_en_tcm314.pdf
I like the old docs that have predictions that were made before marketing got involved and massaged them. The interesting info on page 14 of link above is that the remote climate is designed to use house power when plugged in. I just don't see how the vehicle can use the large traction battery when the relays that connect it rest of vehicle has not been triggered by putting vehicle in READY mode. Rxlawdude says remote climate puts the car in Ignition on state, short of full READY.

Lastly, I remember reading in 12v aux battery threads, that once you have drawn down the small 12v Prius battery it has likely taken damage that will shorten lifespan and lead to more draw down to failure situations. Might be time to get a new 12v.

 

Thanks for your advice as well.

 

Unfortunately there seems to be no good warning for when your auxiliary battery is too low to engage the system. This happened after a surprisingly short time with the car in acc mode. All you will get is an error until you arrange to connect a battery booster or charger.

I'm having the battery checked by the dealer, but if it checks out OK, I'll have to look into some sort of "auxiliary battery for the auxiliary battery." Seems a bit ridiculous to me.

I'm halfways hoping that the battery is in poor condition. That way, the replacement will largely solve the problem.

 

Well maybe if you WERE and engineer you would understand why the design is the way it IS; that is, to prevent an unwise action by the driver or some kind of failure in 12 V systems from also draining the HV battery down to nothing.

THAT would be a lot more inconvenient and potentially more costly too.

P.S. With my recently acquired Ford, if you leave it in ON mode (or RUN) the engine doesn't actually run for about the first 15 minutes and then kicks on for a few minutes. I ASSume it does that to allow some charging of the 12 V battery......which won't happen on ACC.
Don't know if the Prius will do that or not; haven't tried it yet.

 

I'm assuming that Toyota can afford competent engineers. If running down the HV battery "down to nothing" is such a risk, I'm sure that it could be easily protected from too much drain (i.e. 20 boosts in a row) by some simple circuitry that would only allow it to be drawn down to a safe level. Sorry, but it just doesn't add up so far.

 

Greg is right. There is no reason to be sitting, stranded in your car with a dead 12v battery and 2 or 3 kwh of usable power sitting in the traction battery and NO WAY to access it. This is a design flaw or requirements error of the biggest kind. The fix doesn't even have to be some automatic circuit that could be prone to compounding errors. A simple manual mechanical switch that times out and only works once (until the car is started) would be fine.

Example. The car is parked at the airport, a trail-head or other remote place. The traction battery has plenty of juice. Someone leaves a dome light on or any other minor load. You come back to the car and it won't start. Solution: open the hood or trunk, press the "charge my 12v battery spring loaded button. Wait a minute or two. Start the car and you are off. The way it works now is you call AAA or other tow truck and they arrive promptly in 30 or 45 minutes and give you a jump start. Pretty dumb that you have a bigger battery than they have and you can't (essentially) jump your own car.

Mike

 

I think you guys should write a letter to Toyota Engineering and tell them about that great idea.
Honestly.
Maybe they will use it.......or give you a better reason why it works that way in the first place.

It must not be as simple as it appears........because the Ford hybrids and the Volt also suffer from "dead in the water" if the 12 V battery goes dead.

 

This issue has been talked about on Prius chat for years now. I remember reading posts about it dating back to the 2007 model year. It is what it is, Toyota knows how much it pisses of customers but no change in how it works. If you are really serious about improving your lot, buy a AGM type deep cycle battery. It will help some.

 

Doesn't really have to be "deep cycle"......unless you have habits that are known to run it low.
An AGM type of higher capacity likely would be enough for a large improvement.
Alas, fitting it into the allotted space might be somewhat of a problem.

 

It's good to see that some people seem to be taking this problem as seriously as I do. It's good to clear the air about these things, because there's always the possibility that I missed something or got it wrong. As it stands, it appears to be a design flaw that should be addressed. Thanks for all your input.

There is a You-Tube video that appears to have a solution to this problem, which I don't consider to be an ideal one, albeit effective:

I believe the auxiliary battery is already an AGM deep-cycle battery. There used to be a car battery with a small partition, which you could use to boost the dead part by turning a switch. Perhaps one of the business analysts at Toyota believed that this problem was a good way to drive customers to the dealers for service.

This will solve it for now:

 

Uh, I don't think that will work. The cigar lighter isn't hot except when the ignition is on.

A battery tender works though.

 

Good point. I may need to attach alligator clips, so I can boost at the fuse box.

I use a battery tender on another vehicle to keep the battery up when it's parked for long periods. Not sure how it would help this problem.

 

Tha'ts my point exactly, people who want to sit in their car and listen to the radio on acc mode for 20 minutes or so need it.

No it is NOT!

 

And I am suggesting that there might be two other alternatives:
A bigger battery
Make it a habit to do that in the "RUN" mode instead of ACC. (Don't know if that will work for sure but worth a try.)

 

Take a look, there really isn't room for a bigger battery.