Hi! I have a 2003 H. O. The batteries have "Maintainance Free. Do Not Open or Pry Vents" printed on them. I live in Arizona (Phoenix), very dry and hot. I, also, have a 1991 W-250, which, I bought new. That battery also said "Maintainance Free", on it. A wiser man than me told me that that battery was NOT maintainance free. They had put a piece of tape over the six fill holes, to hide them. If you ran your finger over the tape you could see where the caps were. Needless to say, I went home, pulled the tape off and filled the battery, probably extending it's life. I am somewhat reluctant to believe the "maintainance free" warning on my 2003, from my previous experience with the 1991. Do any of you guy's know whether or not we need to take these warnings seriously? Can we top-off these batteries? Thanks for your input. Joe Fihn.