New 12v battery

It does no such thing. The size of the fuse on any of the devices has no bearing on the operation of the power supply.

And it is absolutely possible that the converter is "not keeping up" if it is not operating up to capacity like it should.
That may not be the case here but it IS possible.
And you cannot just blindly say that it is wrong without being there to do further tests.

 

The 12v battery in the Prius is not meant to "run" anything. It simply powers the car on and off. In fact, diagnostics for the DC/DC converter requires switching the car to "ready," and then powering on the hi-beams, and blower to the high position. Then you check the amperage from the 12v battery, which should be zero, and voltage between 13-15 volts.

We also know that the fuse for the DC/DC converter output is only 100A. This means a possible maximum output of 1,300 watts before the fuse pops, which means the converter probably doesn't put out more than about 1,000 watts.

Now that we know all that, if you run a high power audio system with the car in ACC, it will kill the battery pretty quick. The battery is not designed to do this, and there's no reason to run it in ACC when you can turn it to "On," and run the accessories through the DC/DC system.

Additionally, if the audio system pulls more than the DC/DC converter's maximum output, this will start to draw from the battery, and eventually run it down. It will not blow the fuse, because the maximum output of the DC/DC converter is not more than the fuse. The fuse is circuit protection for something outside of "normal." Ditto a car with a standard alternator; It's completely possible to have an audio system that pulls more than the alternators maximum supply power, which will start to drain the battery. IOW, if the maximum output of the DC/DC converter is 1,000 watts, and you're pulling 1,200 watts, the DC/DC converter will be maxed out, pushing 1,000 watts (77A @ 13v), and the additional 200 watts will be drawn from the battery, running it down.

Easiest way to check is to put an amp clamp on the 12v battery cable while the audio system is powered up, and the car is on. If you're seeing current, and the battery is charged, you're audio system is pulling more than the DC/DC converter is capable of, and draining the battery. In this case, your only real option is to run something like a Smart UPS from the traction battery, which can supply up to around 4,000 watts while stationary, as it's power source is MG1.

Of course, I'm assuming this is a high power audio system with external amp, powered with a fused cable directly from the 12v battery. Might also want to check that the amp is not staying powered up when the car is off, also capable of running the battery down.

Cheers.

 

This post nails it. Based on some of the postings here, there seems to be a common misconception that the 12V battery is some sort of power source for the car, that gradually runs down, somehow degrading the car's performance, and needing frequent replacement. This is definitely not true.

The 12V aux battery is just a tool for storing a relatively small charge for the purpose of starting the car (by way of turning on the computer control system), and running several accessory systems when the car is turned off.

The Prius could have been designed without the 12V aux battery, using only the main hybrid battery, but there are a variety of reasons for using the 12V aux battery instead. It handles the slow draw required for accessories like the smart-key and other add-ons like remote-start or security systems. It also provides a sort of firewall for the main hybrid battery, which over time, could be discharged to unrecoverable levels.

 

It is true in some circumstances.
You yourself found that out the hard way........did you NOT ???

 

You're delusional again.

 

While that is distinctly possible, it seems that I remember that YOU were in the habit of listening to the radio in the ACC mode and ended up having to replace your battery because of running it down several times.
Is that not true ??

 

Not really. I was setting up my dash-cam shortly after I bought the car, using acc-mode and it became dead-in-the-water after what seemed like 10-15 mins. At the time I wasn't sure if that was normal, or the aux battery was defective. The dealer confirmed that the battery was defective and they replaced it. I haven't had a problem since, and I now recommend using the ready-mode instead of the acc-mode, because the dc-dc converter keeps the battery charged, and the engine starts up as needed. Ready-mode also seems to shut itself off after a period of time.