When you add a combiner, see how long that alternator runs near flat out to charge two banks. If it keeps your two banks charged and doesn't die, why change? But if it takes too long to charge two banks, that is, your typical run time is insufficient, or the alternator seems to always be pumping out close to 90 amps, and you want near fully charged batteries from engine running time, find out what amp hour rating each battery is: say 100 AMP Hours. Each wet cell battery will only accept about 25% of it's rating in amps...25 amps per battery in this example. If you are charging 8 batts from one alternator and want to charge as fast as possible, 8 x 25 suggests a 200 amp charger would just supply the maximum current for bulk charging. If you rarely run your batteries down below 70% charge,this size should be fine; if you discharge them to 30% charge, not a good approach for battery longevity, likely the next size larger alternator is better. And be sure you use a SMART regulator....they allow faster charging the old style ones. A larger alternator is a generally good choice;the regulator will control the charge current. Then you can begin to worry weather temperature regulation is a good idea...for the batts and the alternator itself... Rob Brueckner Hatteras YF