Press and HOLD for on/off,  and tap button to change modes. [SEP] At first I thought it didn't work, but it works like my bike flasher, not like other flossers.  Press 'on' button for 2 seconds to turn on/off and tap the button to cycle through the modes.  It remembers the mode it was in when turned off too, like my bike flasher.  Doesn't hold a lot of water but very easy to refill.  Can't comment on battery life since I just got it.  Perfect for travel since the nozzle fits inside and it collapses to 6 inches.  Takes very little space on bathroom sink.  My gums have started to receed and dentist suggested the oral irrigator to clean out food debris.  Like this model a lot and I've used several.  Just remember to hold the button down 2 seconds to turn on.