It's amazing to me how much differentiation (wow, that's a big word for me!) there is with everyone's unit! I'd love it if mine could last as long as Mark's.
Like Sinead, mine lasts about 4 days before I get into the 1/2 tank area and I certainly don't want to go past that for fear of it running all the way down without me realizing it. It's a big no-no to let it drain all the way.

I run mine pretty much 24/7 also with the exception that I turn it off once i awhile just to see how long my pain takes to kick in, thus making me ever grateful for this device

Mine takes about 2-3 hrs to charge. I hate it when I've watched a nice long movie and then AFTER the fact I think "Geez, i coulda been charging my unit during the movie!"

Rae