alternator power distribution

Yeah, I've heard of a guy around where I live that re-wires alts... so I was thinkin of having him re wire a stock alt so it'd be able to fit under my hood... and nope, my car's only got a 4 banger but theres not much room any ways... see, I was told like 2 years ago, that there's something exspensive that monitors which side (battery) is low and distributes the power created by the alternator to the low side, thus both batteries charge evenly.... I dont remember what it was called or anything like that...

We seem to not understand Ohm's law very well... THEY WILL CHARGE IDENTICALLY ANYWAY. Thank you, Georg Simon Ohm, for explaining this phenomenon for us!! (Yes, it WAS named after a real person.) Whether connected to the alternator through an isolator or not, they will only charge as needed, and identically. The purpose of the isolator is to prevent them from DISCHARGING equally and identically. You need an HO alternator. I do not recommend rewinding the stocker, what happens if it dies, and you need another alternator right quick? IT DOES HAPPEN, AND YOU'LL BE STUCK. Buy a purpose designed HO product, something built for the duty.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

i understand ohms law to a degree... but what i dont understand is how will 2 different models of batteries (red top and blue top) charge equally?? when they each have different ammounts of resistence (ohms)??? and i understand what an isolator does... i was thinkin about putting each battery on its own isolator and putting a switch on the remote turn on wire (accessory) to the isolators so i can control where my alternator is pushing its power to.... but i was wanting something much more automatic.... can someone help me??? dont forget i'm talking about 2 different batteries... not the same!!