Prius II hi power removable subwoofer install:

Installation

The Prius small ~30 amp-hour 12 volt battery and charging system cannot support a large draw 40 amp subwoofer for more than half an hour or so, and recharging takes 8 hours.
So, I decided to install a separate large capacity 12 volt battery as a separate power source for just the subwoofer. This battery is NOT charged by the Prius, but must be removed from the car and charged in the house using a 120 volt ac charger. The battery is strapped to a plywood mounting board which is placed under the B box, the whole affair being held by tie down straps.
JL Audio - A1400 amp ( 40 amp fuse) & 12W3v3-4 subwoofer
- Atrend sealed B box E12S
- Superstart marine deep cycle battery 90 Amp Hour
- Ship n shore 10 amp automatic battery charger (120 v ac)
- tie down straps, plywood mounting board with slot

Performance
I estimated that the subwoofer, fused at 40 amp, would draw about half that, or 20 amps on average. I was thinking of music with a beat. The sub typically would only produce sound during each beat, then use very little power in between beats.
This proved to be about right. This installation supports about 5 continuous hours of full blast subwoofer use - fantastic base! Then the battery needs to be removed, taken indoors, and charged with the automatic charger which can recharge it easily overnight. And the charger will not overcharge the battery.
Usage
So, if you use the subwoofer during a 1/2 hour daily commute, 2 ways, it will last all week.
Actually, depending on music style, we have found the sub to operate for as much as 3 weeks on one charge, or ~15 hours total use. If the portable battery runs very low, the JL Audio amp has a feature where it automatically shuts down and no damage will result. The portable battery has no effect on the Prius 12 volt battery. The stock Prius stereo will continue to operate. If you are on an all day road trip, the sub can run all day. Just recharge the battery in the motel each night. The deep cycle battery is still functioning well after one year of use.
If you want great sounding base from a full power subwoofer in your Prius, this is a successful way to go. You can remove the whole subwoofer in minutes if you need the trunk space for cargo. And the subwoofer is hidden from site when parked by pulling the Prius trunk cover over it.


Hookup

The music source signal was taken from the rear speaker wires, using running splices just behind the stock stereo head unit. These wires were run under the passenger-side cover panels near the floor and thru the trunk to the battery location. A six way plug allows easy connection of the music source wires along with the 'wake-up' wire. 4 guage wires with an inline 40 amp fuse connect the portable battery to the sub amp. I also installed a ground wire from the portable battery to the Prius chassis to be safe.

Dashboard Control

There is no separate sub adjustment feature on the stock Prius stereo head unit. By setting the JL Audio amp sensitivity and frequency cutoff just right, I found that the subwoofer volume could then be adjusted adequately by use of the rear channel fader adjustment on the stock head unit. Depending on your favorite style of music, it will take a little experimenting to find the best amplifier setting.