Problem: red triangle & red power light when powering on car

12V battery Low voltage or battery about to go out.
Happened to me alot when i forgot to close hatch all the way.

 

If your 12v battery is the original, it's probably the cause of your problems and should be replaced. The other possibility is the brake pedal switch or you're not pushing hard enough on the brake when powering up. I think the 12v battery is really the culprit though.

 

I paid ~$139 plus sales tax when buying the 12V battery from my local Toyota dealer in Tucson this past fall.

 

Make sure you are getting a battery that will fit the Prius and has proper venting. Toyota is really the only battery made specifically for the Prius.

 

My 2005 Prius has been doing exactly the same thing for a couple of months now...very random occurence. We also keep the lights on while driving and have for almost 5 years now. The dealer has not been able to replicate the problem. He must not have experienced a Prius with a worn battery yet. So it's for sure battery replacement time???

 

After 5 years the battery doesn't owe you anything anyway. Waiting for it to finally really crap out is going to increase the total cost (tow, having to go with what the first dealership says when they know they've got you over a barrel), so why not go ahead now anyway? You can shop around, or order a yellowtop on line etc. And you can do it at your convenience rather than have the car die at the worst possible time. At least by a battery boost pack if you aren't going to replace the battery.

 

Absolutely. I've seen a few posts where the hapless owner paid $400 for a replacement 12V battery:

$100 for towing
$100 for "diagnostic" time
$200 for the battery and installation labor

Especially if the battery failure happens to your spouse, SO, or child, who needs this negative drama?

You are not married to the 12V battery. Better to replace it at a time and place of your choice, esp if you can DIY and save all the labor costs involved.

 

All good advice. I did check the status of the battery last night. Without load it is at 9.7 volts. We're shopping for a new one today.

 

Shopping at a dealer? There is no aftermarket direct drop-in replacement. The clamps and perhaps the cables would need modification or replacement. For that matter make certain that the dealer sells you the right one and not some random thing he has sitting around. And make sure he charges it properly before giving it to you.

The fact that the dealer could not replicate the problem is more evidence that some dealers don't know to check batteries or don't know how to do it correctly.

 

Yeah, I found out after 5 or 6 calls that a non-OE battery is not available. I did see the links about modifying the Optima but the part that scares me is rigging up a temporary 12v power source to maintain the memory settings. So far the dealers want $90 - $150 in labor plus the $139 for the battery. If I installed an OE battery myself and lost memory settings what would I need to do to reset stuff?

 

Basically all you have to do is set the pre-sets on your radio and reset the auto-up setting on your driver's side window (easy and it's in the owner's manual). You may also have to set your temperature setting for your auto AC. It's really no big deal.

 

Just curious. Has your gas mileage been suffering for a while now?

It seems a common thing with a bad 12 Volt battery.

 

If you've turned off your reverse beep beep, you'll have to do that again, and if you've set the sks to open all doors, you'll have to do that again too. And your phone contact list. Basically the car's memory reverts to how it was when you got it, except for the odometer of course.

 

Why would a bad 12v battery cause bad mileage. The 12v battery is basically out of the picture when in Ready mode. Therefore it shouldn't impact MPGs.

 

The theory goes that if the battery requires constant charging to get up to the 13+V that the constant voltage charging system provides, then it's drawing energy constantly and can drop your mpgs a little. I suppose this theory could be tested by seeing if the battery is hot after the car as been in ready mode for a while.... all that energy will have to have turned to heat.

 

eLearnaid sells the correct Optima and a complete adaptor kit with excellent instructions:
12 Volt (12v) Toyota Prius Auxilary Battery for 2004, 2005, 2006, 2007, 2008, 2009 and 2010 with installation kit

All reports say that their batteries arrive fully charged, something not all dealers do. Many dealers charge the same price for the OEM battery without installation.

 

You can run the Prius with the 12v battery totally disconnected once in the ready mode. The amount of charging for the 12v battery is negligable. That's why it takes several hours to charge it if it's almost depleted.

 

I was responding to the question of why a bad battery would affect mileage. If a battery can only hold 7 volts, say, a 13v charger will apply a substantial current.

I agree that no current would go to a disconnected battery, and a healthy but depleted battery would climb quickly over 12 volts, so would draw less current and would charge slowly.