Odyssey PC545 dry cell racing battery, in the boot with it's own fuse.

Decent cable (fused) goes from the positive on standard battery underbonnet to the bass enclosure amplifier, then onto the Odyssey (also fused).

Amplifier is earthed to both Odyssey and floorpan (used the spare wheel securing bracket).

Both batteries work together and the rear charges whilst driving.

At some stage the Odyssey will be used on the GTti race car (which is what i bought it for) but for now putting it in the YRV keeps it nicely charged up to prolong life.