All this overcharging and topping up sounds pretty poor to me, even if Oldham did recommend it!
Obviously you can't do that with a sealed lead acid battery, so you need to get the charging voltage right.
I draw a comparison between a car with a dynamo (and topping up the battery), and a modern car with a maintenance free battery + alternator. The key is the alternator doesn't overcharge the battery, it's nowt to do with the battery. An old style battery won't need topping up if used with an alternator.
Times change I guess....!
Chris.