2 batteries

Read through this search = batteries

https://www.the12volt.com/installbay/search.asp?KW=batteries&SM=1&SI=PTB&FM=0&aid=293614&OB=1&Submit=Start+Search

STOP PRESS - the amp is connected to the nearest battery - ie, boot/trunk battery. (As opposed to both batteries next to each other and remote from the amp which is a crisscross connection.) See below if more info needed, or for clarification of 2 "truly parallel" batteries. A second battery for audio systems is usually placed next to the amp (and is AGM etc). Placing a battery remote from the amp does little other than provide longer reserve time - it won't do much to remove cable dips, and a low ESR battery is wasted. (I mention this in case that is your purpose.) If you are running them in parallel, they should be matched batteries and connected as per: (From Rainbow Power Company - Deep Cycle Batteries FAQ - a great company, great information etc.) Normally I recommend against parallel batteries for audio etc (except when paralleled during charging which can be done with most alternators by adding a relay - see my posts elsewhere), but assuming your batteries are matched (same type, age, batch, condition) and located together (same temperature), and with the connection above, you have the most favorable parallel situation. [2 batteries in parallel have at least TWICE the failure rate of a single battery (where failure rate is for internal cell collapse and failures that will cause discharge of the 2nd good battery).] Hence running loads from parallel batteries, you run them from the +ve of one, ad the -ve of the other.      And now re-reading your OP, I see that you probably have the 2nd battery in the rear (good - that's better!).... Then they should only be paralleled when charging. And your amp is connected to the nearest battery. (That should be obvious.) The advantage with the near-amp 2nd battery is that only the wiring between the 2nd battery (ground & +12V) to the amp need be fat (low resistance) - the alt or 1st battery to the 2nd battery is less critical - unless you want full voltage from the alternator (ie, the alternator is large enough to supply the amp and keep it above the full-battery voltage of ~12.7V).

This was probably all covered in the post above...

oldspark wrote: And your amp is connected to the nearest battery. (That should be obvious.)

...when you have a second battery dedicated for the sound system, it is already connected to the primary battery.  You would connect your amplifier to this second battery as it is nearer to the amp.  This keeps wires at their shortest.

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

PS - I liked some of the threads found under Anon's search string. I loved the one about running 2 alternators - some people just don't get it. (your don't "just" run 2 alternators to the same system. 2 alternators for 2 different supplies or batteries - yes, but not a commoned battery or supply!) Then there are others that mention older methods - eg smart isolators etc, when a charge lamp does the same usually better, more reliably, and cheaper. Else a voltage sensing circuit with timer (ie, smart solenoid/relay/isolator). But as to alleged current sharing or charging priority; and diode isolators.... Oh well, I came along well after them (I think!).

thanks everyone, so basically i should parallel the two batteries and get the exact same batteries, correct?

No.

Use a relay. And have the appropriate protection (ie - fusing at each end of the interconnecting hot wire). The "Charge Lamp Terminal" is labeled "D+" on most single-wire alternators, and "L" on others. If your alternator does not have a similar chargeLamp circuit, a voltage sensing circuit (with appropriate time delays) can trigger the relay - that's what commercial Battery Isolators tend to use.    I thought I had relevant writings here on 12Volt, but most seem to be on other forums.... (One day I'll organise a better diagram.) To recap what I said earlier, batteries should not be paralleled (except when being charged, or being used for a specific purpose - ie, not just left connected together.

alright cool, thanks man