The W-Fat has one, don't leave the dock without one!!
I run mine off a seperate battery, it will go 20 to 25 hours before recharging. I did buy a small solar panel that I hitch to the battery when I'm at the dock, which helps maintain the battery longer. TnT W-Fat (will be on winni Fri. 9am ish till Sat. noon ish on #12 say hi)