Expert: Peter G. Lee - 10/14/2006

Question
 I have a 750 cca  940 ca car battery and it drains because of my system.  I have two ten inch subs and a 900 watt amp.  I was wondering what i can do to make sure my system does not constantly drain my battery because ive replaced it far too many times now.  Is there something i need?  Anything will help because this is quite frustrating.

Answer
Hi,
I would fit a separate high capacity battery (at least 75 amp hour) with a split charge relay just for the audio.

Locate the second battery securely near the amps and hook them all up as usual.

Run a 60amp (minimum) lead from the Car's battery to the new one's positive with an inline fuse right next to the car battery terminal of 50 amps  and earth the other side of the second battery to the chassis/body.

Fit a heavy duty relay of 75a 12v near the cars battery and cut the new lead just after the inline fuse and fit to the input and output connections of the relay.
(So, car battery, in-line fuse, relay, cable , second battery, ok?)

Connect one side of the relay’s solenoid to earth and from the other side run a thin wire to the thin wire on the alternator, this gives 12v only when the engine is running (and to the ignition warning light) so when the engine is NOT running the second battery is disconnected from the car's electrics and ONLY powers the subs etc, as soon as the car starts the alternator pumps power into BOTH batteries and recharges the second one as well as the car's.
O.K.
Please leave feed back so I know how it went.
Regards, Peter