Any charging in excess of enough milliamps to maintain float after the batteries have reached OEM electrolyte density will electrolyze water needlessly. Determining that point takes some effort but it is worth it. It minimizes excessive positive plate shedding. When charging by generator I factor in the cost of the fuel versus "ideal" charge rate by the worth of the battery. "My ninety dollar battery lived twenty percent longer and it only took a hundred dollars in extra generator fuel to do it" does not cut it in my book.
5% antimonial batteries electrolyze water "easier" than lower percentage flooded lead antimony acid batteries. Part of the master-plan tradeoff and compromises of choosing one battery type over another.
Higher charge rates and ambient temperatures accelerate watering needed.
