Audio Systems: ADVICE ON WIRING OF AMP

Question
I have a 1995 Mazda 626, with a factory stereo (currently looking to buy and replace with a better CD player), in our trunk we have a 700 watt amp with 2- 10 inch pioneer sub woofers in a dual box. We had it professional wired and it is hooked up to our main battery up front under the hood. Lately our battery has been dying off and on and more than likely we think its cause of our amp (maybe?).  We were considering putting a 2nd battery in the trunk or maybe find room somewhere in the front (if possible) to run the amp off of by itself.  I am looking for the best solution on wiring our amp to a 2nd battery. We have a battery from our 94 Mazda 929 to use. Should we put the 2nd battery in the trunk and if so how do you go about holding the battery, mounting it, & be installed safely and securely?  Or should we find a way to put the 2nd battery under the hood also (if its at all possible and since its already wired professionally to the main battery up front) and then just hook the amp wires/cables to the 2nd battery that way if we can make room under the hood for another battery?  Any help, advice and/or suggestions would be greatly appreciated.
Thank you so much for your time.

PS. I can't think of the type of Amp that we have right now, its an older model, but we were told it was the best made.  If that information is important I can get that for you.

Answer
Second batteries are generally not a good idea because of the disparity it throws to the charging system of the car.  It can cause current imbalances to the charging currents that confuse the charging circuit and electrical system of the vehicle.

Better solution would be, I propose, to purchase a new, high output battery.  The 700 w amplifier should not be a great load with a good strong battery as long as you are not playing the system with heavy bass going full power constantly.  If you are running continuous heavy output you may need a heavy duty alternator in addition to a bigger and higher output battery.

That is my opinion.

C