New 12v battery

Whatever the problem is with your 12V battery, it isn't caused by running in EV mode. The Prius has no alternator, and the 12V battery is charged from the traction battery whenever it needs it, regardless of whether the engine is running or not. As long as the car is in Ready mode, even when parked, the 12V battery can charge. What does kill the 12V battery is using it in Accessory mode for more than a few minutes.

There have been mixed reviews here recently on the Optima YellowTop batteries, with some members reporting batteries received partially discharged, and others finding relatively short lives on new batteries. A search will pull up many threads.

 

If that fails, try 9 EverReady "D" cells in a cardboard tube.

 

I have a Gen II, not at a C (so it might not be apples-to-apples), but I recently found the OEM battery at a metro ATL dealer for $160 + tax. They had a Black Friday special for 20% off parts & service during Service, but I persuaded them to give me the discount for parts from the Parts desk. Second choice would have been Optima from Amazon, but I got a little antsy given some of the feedback on the board here.

 

could it be the audio system?

 

.

 

Obviously. As I said in another thread, I ran my battery down to. "no start,blank screen, no lights. And then just jumpered it with a 12V I keep in the Garage. And no more problems. I have done this FIVE times with the C and each time = full recovery. Why 5 times, I keep leaving the keys in the ignition, and Off. My other car is a PIP. I am amazed how good the battery recovers // does it really not run down ??

 

maybe they put a limiter on it?

 

. Yes, it's very possible they did something........useful......finally............on the 12V

It would be nice if Toyota communicated.

 

we can only dream...

 

First, your car does not have a conventional alternator. The battery is charged from the main HV battery any time the car is in RUN mode.

Second, a lot of owners have found the replacement OEM battery to be of good quality and respectable life. Using IT would not have cost you THAT much extra and would have saved a LOT of time. In addition, several others have reported problems with short life of the Yellow Top that you ended up getting.

And finally, new batteries need to be fully charged at the beginning. If you haven't done that already, it is not too late.
Also the charging voltage should be checked.......just incase your extra load has messed up the DC/DC converter that actually does the charging.

 

I already made my rant about Optima, but suffice to say, beware of those companies which have been bought out by their competitors with a goal towards removing the competition.

 

You could put a Ammeter in series with the 12V battery and read the current draw, normal state, in accessory, and finally in ready. Compare the three currents, especially with your sound system ON. Compare the three readings. In accessory mode w/ the amplifier on, it may be pulling too many amps. In ready it may be OK.
In Generation 2, we had a few people run thier battery down just listening to the radio. While parked!

 

It's possible, but rare for the stereo to work while drawing excess current. Usually this will make a component fail, or get very hot, in which case you would probably smell something wrong.

It's very unlikely that anything could draw enough power to exceed the capacity of the DC converter, in which case it would trip a breaker. Its remotely possible it could be that the converter is failing, but that's unlikely without a warning.

My 12V aux battery was bad when I took delivery of my vehicle. It went dead after barely 10 minutes in acc-mode. The dealer tested it and found it faulty, and replaced it. Since then, I don't use acc-mode. It's much easier to just put the car in ready-mode. The battery never goes dead that way, and the engine runs very little, but it does when needed.

 

In the context of this discussion, "excessive current" means more than the 12 V charging system and battery can safely supply.
The assumption is that the new stereo is designed to pull that much current.

 

In this sense, I meant that the stereo would be drawing more than it's rated to draw, due to an internal fault.

 

Running any high-power device from the 12V system without connecting it through a suitably-sized fuse is just asking for trouble.

 

And that lends even less credibility to the theory that the DC-DC converter may not be "keeping-up" to the stereo. Basically, the idea is wrong.