More power

I belive I need to add another battery to my trucks power system to handle the draw requirements my system and accesories currently have.  Is there a battery management device that is recomended?  I can come up with the hardware to mount the 2nd battery easy enough but efficiently managing the power and charge from the alternator would be key before I buy something I don't need or do need. The vehicle is a 00 k2500 silverado classic with a 5.7 eng.  Don't yet know what the alt output is.  After a year on the current config I have  recently run into a voltage problem at high volume levels that my head unit does not appear to like as it seems to be shutting down the remote turn on lead for the amps.  I have been watching the voltage level drop from my power grid for about three weeks until I ran inot this problem last night at or about 13 volts registered on the amp and head unit screen.  System: Alpine CDA-9835 Head - Alpine MRD-M501 Sub amp-Alpine MRV-F340 mids and highs to Infinity Seps and plates and 1 each Alpine SWR 10" Sub in a q-logic enclosure (modified to fit sub).

A second batt will help when playing your system when the truck's motor is not running, but to get the best of your elc system a new high output alt is were you need to start. 200amps and 2 good batts will be a good start.

Thanks for all the feedback.  Turns out is was a faulty primary feed fuse holder under the hood.  The unit had small cracks in the polycarbonate housing that allowed water to get inside and corrode the push in connection at the glass fuse.  I replaced it with a blade fuse config from Rockford Fosgate and watched my voltage problems dissapear. 

Thanks again.