12 Volt Battery Problems

Prime suspects:
- Somebody isn't closing all the doors and hatch, or shutting off all the cabin lights, or shutting off the car completely
- Somebody likes to use the radio or other accessory with the car in ACC or IG-ON instead of turned fully ON and Ready
- Some aftermarket electronics is junk and/or wasn't installed correctly
- The car is not driven long enough often enough to fully charge the 12V battery

 

As your title indicates, the 12V battery is the most likely suspect. It sounds like the car is getting plenty of use so the battery may just be defective. Can you get it replaced under warranty?

 

Voltage should be 14.1 not 12.5 while driving. I'd bet on the battery not taking a charge before betting on the car not trying to charge the battery.

 

Very interesting. What is your means to monitor the voltage?

I would expect that when the Prius is READY, that 12V bus voltage would be ~13.8V - 14.0V. I've noticed on my 2007 that after some time elapses, the voltage may drop to 13.4V if electrical accessories are not in use. Your voltage readings are substantially lower and that would help to explain why your battery is becoming discharged despite all of the miles that you drive.

You mentioned that the car logged a low-voltage DTC. With that in mind as well as the symptoms that you described in your OP, my guess is that the inverter needs to be replaced because the DC/DC converter is not doing its job.

I suggest that if you have a decent digital multimeter available to you (Fluke is a reputable manufacturer, for example) that you use that to confirm the voltage reading of your in-car device.

I also suggest that you use the current measurement function of the DMM to see what the quiescent current draw is, when the car is IG-OFF and all doors and hatch are closed. It should be ~20 mA which fluctuates as the security LED goes on and off.

You can measure this either at the 12V battery negative terminal or at the dedicated positive jumpstart terminal. If the former it is easiest to disconnect the battery cable where it connects to the body. If the latter you would have to remove the 10 mm nut located at the jumpstart terminal, then lift up the wire which provides +12V to the main relay/fusebox and put the ammeter in series with that wire and the jumpstart terminal.

 

I have a 2010 Prius II with just under 22,000 miles. It wouldn't start this morning. The dash indication flickered something about putting it in park. Is this a dead main battery just like the one I have in my Camry? I can't get the car into neutral to push it out of the garage. I don't know how I can have it towed? Any others with this problem. It is under warranty to 36,000 miles. I wonder if the battery is under warranty?

Helpful comments are appreciated.

Michael in Ohio

 

This sounds like the 12V auxiliary battery is dead. (The traction battery is sometimes referred to as the "main" battery, and that probably is not the issue here.)

To get the gear selector into N, it will be necessary to apply 12V so that the ECUs can be powered up and the parking control ECU can release the parking pawl.

If it is not feasible to do this, the tow truck driver will probably just drag the car out of its parking area, regardless of whether the gear selector is in P.

The 12V battery may still be under warranty, you might consult your maintenance and warranty guide so that you don't have to guess. Good luck.

 

An extra long jumper cable might be your best bet. Good luck.

 

I have a 2004 with 103,875 miles on it and the start battery finally has died.
The dealership told me 6 months ago that it looked weak but I told them that I
would take care of it myself.

I logged onto the internet in search of a replacement battery and found the best deal at elearnaid.com
I ordered the battery on Monday and I received it the next day.
The Optima battery ships with all the parts necessary to convert
the battery posts and hook up the venting system.

The install took about an hour and I saved major bucks over a
dealer installed battery. The Toyota dealer wanted $213.45 plus tax
for the cost of the battery, plus labor, which is billed at $95 an hour.
The total estimate was $350 and I’m sure that they would not be installing a battery that is as good as the Optima battery that I purchased.

The cost for the battery was $170 plus tax with free shipping.
These folks have what you need to replace your start battery
and save yourself some major bucks.

 

Optima now has a no extra parts drop in battery, fits nicely, no problems installing. I just installed one, and it was very simple.

 

Where did you buy yours? I might need to get one in the near future.

 

Slightly off subject. I recently replaced my 12v battery with one from the dealer ($166). I may have pulled the trigger early. The one I pulled out still reads 12.4V after two weeks on my work bench. Does anyone know where it can be recycled or better still used till it finally dies?
I didn't have any problems just wanted to replace it before it's 6th winter.

 

If you take it back to the dealer where you bought the new battery they should give you a refund for the old battery core. You should see a Core Fee on the invoice for the new battery.

I just bought a new battery for my wife's Honda and it had a $16 Core fee that was deducted since I had the old battery with me.

 

Junk yards will pay by the pound for your battery. I've gotten $8 for one. My Toyota dealer did not charge a core fee the last time I bought one for a friend.

 

I find myself in a similar situation. My 08 Prius won't start, most likely from a drained Aux battery (my fault for leaving the car with the SKS enabled). I'm in Australia and my car is being stored at my parents house in Washington state. I'm trying to get my parents some help to get the car started. The car is parked where they're unable to jump it. Would hooking up a trickle charger for awhile recharge the battery enough to get the car started?
Thanks.

 

Georockc, it can be jumped from the battery in the trunk or the jump point under the hood. With portable jumper packs now, jump starts can be done in almost any situation. A trickle charger may very well bring it up to a point it can be started, but personally, I would disconnect the battery first so as to not apply trickle charger voltage to the car's components.

 

Yes it will work, I had to do it for a friend with an 07. For safety's sake I disconnected the battery cables before charging, and it worked fine. When I got the car started I took it for a nice long drive and 2 years later it's still going strong.:rockon: