New audio install in 2007

I would trust Crutchfield. The Prius has a wimpy 12V, no alternator and gets all its 12V power from the Inverter.

 

I'm running (2) 4 channel amps with no problem. 0 gauge and a 100amp fuse going to distribution block then 1200RMS total draw from the 12v battery.


iPhone ?

 

The Prius' inverter has a 100A fuse, so it's been surmised that it produces about 80A maximum. When the Prius is on, the Prius computers and base accessories (e.g. brake pump) draw around 20A. With the headlights on, this can increase to around 35A. The air conditioning system can draw another 20A. That leaves around 25A of capacity for an audio system without draining the battery. 25A * 13.8 volts = 345W, however class A/B power amplifiers in cars are usually ~60% efficient at max power, therefore 345W*.60= 207W max amplifier power. This is being fully conservative, and probably approximately how Crutchfield came up with a 20A number.

However if you don't have lights, A/C, or any other accessories on, you have ~60 amps to use without causing battery drain. 60A * 13.8 Volts = 828 Watts, or about 500W maximum output to the speakers after amplifier power loss. Going class D (higher effeciency amps) will get you a bit more.

If I already had amps with a much higher capacity, I wouldn't worry too much. You can avoid going into a battery drain state by not running your system at maximum volume. Keep in mind in audio that every 3db increase in volume requires double the power, but it takes ~10db for something to sound twice as loud. Therefore if you keep your maximum volume 6db below maximum of your amps, you'll only draw 1/4 of the RMS power, and it won't even sound 1/2 as loud.

If you're worried about your battery, you can use a battery voltage monitor such as a scanguage. The inverter in the Prius puts out 13.8V. If you see the voltage drop much below this, it just means you need to turn your system down a notch or two.

If you don't use a voltage monitor you should be fine - this guide should keep you safe:
If you don't have lights or AC on - run your system up to really loud, but not f****** loud.
If you have the lights on or you're using the AC, run your system loud, but not really loud.