My previous comment wasn't directed to any specific person, just an observation noted from reading all the posts.
JJ, not sure what you mean by "most any regulator". Are you talking about Yanmar and sim systems or that generally associated with automotive charge systems? If the later, I have to agree with SPYDERLR's comments. One comment you made if you are talking about the Yanmar system is, there is no field winding. I also disagree with your comment about being OK to have voltages up to 15V. That's way above the point where a nom 12v LA battery would be happy. A typ automotive charge system doesn't go much beyond 14.25V. Any charge voltage above ~13.9 can be an issue. Voltage and duration will determine what happens. Can be as little as overcharging, i.e. boiling of the electrolyte, to shortened life.
You gave some of your background so I've give mine. A retired Eng from HP. In the mid-80's I did some research on LA batteries for use in portable medical equipment. Based on that work our equip moved from Ni-Cads to LA and the whole industry followed within a few yrs. Not claiming to be an expert but I', more than familiar with care and feeding of LA batteries and typ charge systems.
If the Yanmar alternator does not have a field winding, what does it have to induce a field.
Even if the regulator is separate from the alternator, the grounding of the alternator and regulator is one of the paths for voltage and current.
This statement has to do with battery chargers.
Many modern chargers are charging wet cell batteries at much higher voltages than previously. 14.8 to 15 volts is becoming common. This increases the charge rate and performs a mild equalization charge. It is not recommended that such a charge voltage be used from an alternator as the alternator does not have the ability to drop to a lower float charge the same way that a dedicated charger does.
Another observation that I have made with Ni-Cad batteries is that on an 18v DeWalt charger, I have measure the charge voltage at 24 v. A 12V charger will charge at 15-16 v.
I really see no problem with charging at a higher voltage, because if the system is well regulated at say 14.2v, it may start out at 15v, and as the charge builds up to the regulated voltage, the amount of charge tapers off.
How many of you have used the 125 amp mode on some of those large chargers to get a fast charge on a battery.
Yes, I agree that if left on for a while, the water will boil out, or the sides will bulge and maybe explode.
Do you have a schematic of a Yanmar charger system?
If the alternator goes out on my Kubota, I think I would replace it with a small one wire Ford alternator. Way cheaper and will allow more acessories.