Hey guys so I'm new to this forum (with experience on installing car audio) and I'm getting another car soon and I want to make the sub setup in the new car top my previous setup. First, let me tell you about my first setup, I had was a 2014 honda civic which had a Hifonics Brutus 15 inch rated at 600w rms and an Alpine MRP-M650 also rated at 600w rms. I spliced into the rear speakers for the amp input cause i had the stock radio and I didn't need rear speakers if I'm going with a sub setup. That setup was really good but the headlight dim was BAD. I was using 8 gauge wire and a 80a fuse (the wire was wayyyy too thin for the power i was running, I only used it because it had actual terminals on it and bare wire was janky and fragile). The car has a 90a alternator and the sub murdered a perfectly good 4 year old 410 cca battery to the point where the car will barely crank in cold weather in about 6 months and the battery will die if i leave the key on for more then 2-3 minutes. This next build I am gonna do the entire install properly with no hackjobbing. The next car I'm getting is an older Subaru Outback which also has an alternator of the same rating but a larger battery and my goal with that car is to run 1000w rms or more with 2x12s without causing the headlights to dim. I plan on running a proper double din and doing the Big 3 wiring upgrade with 0 gauge and run 0 gauge power wire and ground to the amp but then the headlight dim could get even worse then before due to the amp being able to suck more juice from the alternator and starving the other electronics. Led headlights will help reduce overall power consumption and not dim but the voltage dropping due to the bass hitting will still be a major problem as it's not healthy for the car's electronics. What would be the most cost-friendly route with preventing headlight dim for a 1kw rms setup because I won't be able to afford an upgraded alternator for awhile (everyone knows that Subaru parts are expensive and harder to come by usually). I could do a second battery as those aren't super expensive plus ill get the benefit of some extra cranking power when it gets super cold and with 2 batteries i can simply run a power distribution block and run 4 gauge to the amp because my amp has a 4 gauge power and ground hookup. Another option is a capacitor but I have no clue what size I need. Can someone point me in the right direction before I embark on this project, I really don't want to be murdering car batteries every few months with the subs every time I want to play some tunes.
Heres a parts list of what I'm planning on getting.
Subs (2 of them): https://popsspeakers.com/products/p1000-12
Box: Buying with subs preinstalled from a friend and its brand new never hooked up
Radio (buying used from a friend for cheap): https://www.amazon.com/Kenwood-DMX7704S-Digital-Receiver-Bluetooth/dp/B06XTYJTMQ or this if my friend decides to not sell the kenwood: https://www.crutchfield.com/p_1302440NEX/Pioneer-AVH-2440NEX.html
Also if anyone is curious, here's a vid of the headlight dimming issue I'm having on the civic, the dimming gets worse while driving cause the stock radio has a speed sensitive volume feature that I left on. Also, the song I chose doesn't have a big bass drop so it doesn't seem like its bad but it really is bad: