Adding big amp under seats. Run cable from inverter?

For anyone serious about installing an amp like this in a Prius, the 12V system would have to be upgraded accordingly. My guess would be that it would more than double the cost.

 

Not necessary. My battery and system are 4+ years old and counting.

 

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Just something to throw into your calculations.
You are assuming that the voltage drop from the dc/dc converter along the supply wire will leave the voltage at the battery lower. The battery voltage however is monitored by a sense wire going back to the converter.
If the battery voltage is sensed low the converter increases it's output to compensate until the voltage measured by the sense wire at the battery is at the correct level. There will always be a voltage drop in the converter supply wire depending on load, but the voltage at the battery will "within reason" remain at the required charging voltage.
This effect can be seen by monitoring the battery voltage on the MFD in ready mode. If you turn on the headlamps the battery voltage does not fall in fact it often goes up as the dc/dc converter sees the voltage drop via the sense wire and compensates. The load on the dc/dc converter with the car in ready mode and the lights on is around 30 amps depending on the state of charge of the 12 volt battery. This is without any other accessories running.

John (Britprius)

 

It's not polite to judge, but when you see someone rushing headlong into a mess, it's only right to say something.

 

I did completely understand the ironic humor in you rely.
I think Greg has possibly misunderstood your remarks due to slight differences in in humor between the continents. No disrespect intended towards Greg in that remark.
England and America two great nations separated by a common language.

John (Britprius)