voltage drop problem, what battery to buy?

Are you both suggesting that wiring is my only issue and I don't need to upgrade my battery nor my alternator?

You will need to check it.  You must be playing it at the level in which you got the 1.5 volt drop.  Playing it at a lower level is not going to tell you anything.  Is it a fused distribution block?  If so does it show any signs of melting the plastic around the fuse holder mounts?  Checking from one end of the distribution block as he suggested will tell you if the distribution block is your problem.  That test can be done in less than a minute.  Once again, the system must be PLAYING to check this too.

i am an idiot wrote: You will need to check it.  You must be playing it at the level in which you got the 1.5 volt drop.  Playing it at a lower level is not going to tell you anything.  Is it a fused distribution block?  If so does it show any signs of melting the plastic around the fuse holder mounts?  Checking from one end of the distribution block as he suggested will tell you if the distribution block is your problem.  That test can be done in less than a minute.  Once again, the system must be PLAYING to check this too.

The Distro bock is fused and it uses ANL fuses, so your saying I should be looking for melting on the plastic around the centre of the fuse or burn marks on the fuse itself? The amps run at 12 V when at no volume, but when I turn it up to 52/60 on my deck its sitting at 10.5 V. (I probably should have mentioned that before...)

Earlier I asked if the 10.5 was at the battery or at the amp.  I do not know if I ever got an answer.  If that was the reading at the battery, performing the tests above will tell you if there is a voltage drop on your power wire or your ground path.  And it will tell you which of the 2 is more the cause.  If the voltage was 10.5 at the battery, you have charging issues.

i am an idiot wrote: Earlier I asked if the 10.5 was at the battery or at the amp.  I do not know if I ever got an answer.  If that was the reading at the battery, performing the tests above will tell you if there is a voltage drop on your power wire or your ground path.  And it will tell you which of the 2 is more the cause.  If the voltage was 10.5 at the battery, you have charging issues.

I thought I said this clearly, but it was 12 at the front, and 10.5 at the sub amp when I was running 52/60 on my deck (cranking heavy bass).

If what you stated is going on your wire is the problem. If you got cheap wire you get cheap results. Turn the car off check both ends of the wire and post your results. Another tet you can do is unplug the wire from your fuse to your distro block run a new test wire from your fuse to your distro . Have the wire outside the car for a easy test turn it up and post your resaults. I think your main amp wire is bad.1993 sdv

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i am an idiot wrote: I am sure you did mention it, there are a lot of posts to read through.  Performing the test at the distribution block should be simple.  One lead on the input of the block.  the other lead to the output side of the fuse leading to the sub amp.

So I hook up a multimeter like you mentioned, and what do I look for? I do this with the volume cranked up right?

You use you voltmeter or multimeter to find your biggest voltage drop - eg: * in the ground circuit: chassis to engine block; battery- to chassis or engine; chassis (or whatever) to the amps. * in the power circuit: alternator to battery+; battery+ to front/nearby fuse or distro block; across fuse/distro; distro to amps (or front fuse to rear distro; across distro; distro to each amp/load) etc. IE - find the voltage drop across each section. Tackle the biggest drop first. Doubling your copper (cable) across that section will halve that voltage drop. That's your cheapest option. And reducing that 1.5V drop is VERY worthwhile. (That's 150W lost per 100 Amps of load.) You might then consider boosting your source voltage from about 12.7V to 13.8-14.4V with a bigger alternator.