I will be running a FI BTL 15 d2 off of an Orion 2500d. Box is about 4 cubes tuned to 34z. I have a 180 amp alt, an optima yellow top for front battery, and a batcap 800 for back battery. I will have big 3 done in 2/0 welding cable.
questions:
1. Is it worth having multiple runs of 0 gauge from front battery to back, or will 1 be enough?
One would be ok, but multiple runs wouldn't hurt...
2. Is it worth getting a second batcap for my trunk, or should I install what I got, see what my electrical is at, and just go from there?
Yes. That one 800 is not going to cut it. Wait...what are you wiring the amp to? If you're wiring it to 1 ohm then no way in hell. Also, if that Yellow Top is under your hood as a starter battery you might as well replace it too. Deep cycle batteries will ALL die eventually if used as a primary start up because they are not designed to discharge/recharge like a regular AGM lead-acid.
3. Do I need an isolator inbetween batcap and optima?
Not unless you plan on running your system with the car off a lot.
4. Do I need to fuse between Batcap and amp?
