I only have a 60 amp alt. and i was wonder if it's okay to put a second battery in the back of my car like a kinetik hc 1800, will it be able to charge my stock battery and the second bigger battery in the back? i'm just running 1000w rms.

i'm thinking of a second battery because i'm planning to get a new car next year, so a second battery will be easier to transfer to the new car, then a bigger alt.

If you run more battery instead of alternator you will get 12v for longer (assuming you crank it and use more power than your alternator can make), so lets say after one song it dies back under 12v and you lose volume; with two batteries it will run 2 songs before it dies out....depending on what battery you get/etc. It will have more capacity to hit bass notes in general. With more alternator you will be closer to 14v but on hits the alternator can't react real fast anyway so thats why you still need more than one battery....depending on how much power you draw and what battery of course. But the alternator will tend to keep it 12-14v range (indefinitely) not 12 and then below when you completely outrun your alternator and the batteries go down. Some systems I worked on back in the old says we ran three batteries, the largest alternator was 60-90a and would not run all those AB amps like LP 5002s/etc. They would hammer for a few songs and then you had to give them a break. This is all for music use. For music you don't often keep it hammered for that long anyway so you just add enough batteries to go long enough for you.

Your alternator will charge both fine, but will take longer than one if you run them way down. Except for the big bass hits you will run on the alternator at 13.5v or so. Once you draw too much and it can't keep up you drop to the ~12.5v of the charged battery, but then have both alt and battery for power. If you go way over the alternator you will be more and more on the battery alone and eventually its voltage will drop lower and lower....more batteries just make that part take longer. That might be an easier way to think about it. At 10-11v your amp might shut off and the car might not start.

I would just upgrade your under the hood battery and be done if you plan on moving to a new car.