Whole heartedly the charging system and its performance relates directly to battery life, performance and in the case of wet batteries, the loss of water. No matter if a charging system is working 100% correct, a wet cell battery will loose water, no way it can't happen, the H2 gas is produced in the charging state and it comes from the water in the battery. The venting of the gas carries as hitchhiker wet solution, which is the cause of corrosion on cables so common in the old wet cell systems. An over charging charging system due to a bad voltage regulator will increase this loss of water and out gassing to the extent I have seen batteries blow up like balloons even explode. Working on a car one time I had a customer with a lit cigarette lean over my shoulder to see what I was doing while I was quickly trying to shut the car off as its battery was expanding and contracting like a set of lungs. Plenty of H2 being produced, (no smoking in the shop but some people think they are special). Turns out his voltage regulator was defective and he was getting full charge of 24 volts off his alternator along with 100amps.
Ok a long story, even the best charging systems are not perfect with wet cell batteries. Climate also had a lot to do with their off gassing, hot days, they produce more gas. The rule of thumb for car charging systems is 13.8 to 14.8 volts, I would quibble that one or two tenths of a volt lower would be the range for a BMW airhead. So say 14.5 volts or so. Even at that setting or lower, you will still loose water. Hey some of us get lucky and can go for months without a great loss, others like me while I didn't loose a gallon of water each week, I did check regularly because hey, it is part of keeping things in shape to check the battery, especially one that uses water.
The way to go is the sealed gel batteries, while they are not perfect either, they are a whole heck of a lot less trouble and worth every penny in my mind. One thing I don't have to worry about now is water level in the battery and the battery connections and box are clean, no more cleaning with baking soda and water.
Wet cell batteries are old tech, and while cheaper in price, I myself don't think they are cheaper in maintenance. Cheers, St.