Batcap vs. 2nd Battery

Hey guys, long time listener, first time caller!!  Long but quick question.

What the heck is a Batcap? I mean, I know "what" they are, but what exactly do they do? I have heard they are a battery, a capacitor, a battery that acts like a cap, and a cap that acts like a battery. What do they do?

Also, would adding a second battery be better than adding a batcap? I currently have a 3 farad stinger cap also. Should that stay or should it go? And what would be the best battery in my case, I plan on leaving the stock under the hood.  I don't have the money right now to upgrade my alternator, the only thing I could do is have it rewound to 140A, but then I could not do the Batcap or Battery thing>I believe that with my current amp (Eclipse 34230, 370w X 2) on my components it will probably only draw like 40-50A on the top end (rated at 100A max) and possibly a Tru H-1 Hammer on my sub (running 1.2 ohm load, I was told for music it would only draw like 80A on a regular basis with music). So I figure probably my draw will probably be like 130A with music play. I may do some comps, but nothing hard core, just to see what I hit and for fun. So, in my situation, Batcap or Second Battery and should the cap stay??Sorry this was so long, but I tried breaking it up so it was easy to follow. Thanks!!!

honestly I would have to say go with the larger alternator, and not even a rewind unless you are sure of the shop that is rewinding...alot of the time the rewinds will give off some pretty annoying hiss because they dont always upgrade everything they should during the rewind process... batcaps are more for competition use than a regular ongoing supply and demand situation...you should be able to get a high output alternator for a reasonable price depending on what car you have...I would almost bet you could get one for less than u paid for the 3 farad cap... I would make that the eventual goal much more than anything else...I would invest in a good solid high output alternator, maybe 180A, and ditch the 3 farad cap and live happily ever after...caps are more for voltage regualtion than for a hardcore power demand situation...they are typically just a stress point in any high current stereo... and with a 180A alternator, you wouldnt have to worry about whether or not you were going to compete, cuz you would have the power regardless... sorry I couldnt give you the answer you wanted to hear, but the alternator really is the foundation of any stereo, and you want a strong foundation for anything you are going to build in any field...

a batt cap is a batt and a cap. i love them. Big Dave