Just curious but, if I were parked, engine off with the ICE playing (can't imagine why I'd be doing this, nothing to do with being in the back seat's or anything I'm sure ) but just supposing this scenario occured, how long would it be before I wouldn't have enough battery power left to start the car? Given 25w RMS per channel head unit 130w RMS amp with 12" sub and cd changer.

 

How many amp hours is the battery?

 

Dunno, how many amp-hours does a standard Euro-Scooby battery have? It's not been upgraded.

 

Most car batteries are roughly 50-70Ah. Which means about 720W for an hour. Divide 720 by current drain and there you have it. Look in amp/head unit manual for max current draw - or double output of amp (***. 50% eff). Or add up fuses - my headunit 10A (must take less!) and amp 40A max poss 50A - therefore I would get twitchy after 1 hour at reasonable volumes, but you might get 2 at low volume. I had a friend back in school days whose PUG 309 battery flattened in 15mins with his system on!

 

...and if you're playing Barry White to sooth your lover then there'll be loads of subwoofer action just from his voice = loads of current draw.

If you're planning on doing this often then it's a good idea to get a second battery and a big momma of a relay to isolate it from your starting battery... Autoleads do a relay for about 20 quid.

 

I've got a 12 volt motorbike battery lying in the garage, might look into hooking it up.

Cheers guys