I recently installed two new Hitachi 80 amp alternators on two Yanmar 3HM35's. The alternators have one wire from them to the battery. They are internally regulated.
My question is whether or not I should be installing some kind of a regulator between the alternator and the battery. I worry that with the solar, wind, and these alternators I might cook the batteries a bit when running both engines.
Your two Hitachi's won't harm your batteries, but won't charge them very fast. I don't recommend converting them to external regulation. You are better off with one or more high output alternators and external regulators if you need heavy currentcharging.