(I have been electrocuted. Not something I need to do for fun.)
Tried 240v once, not keen to try it again.
My first TENS had a tendency to short-circuit painfully if the lead detached from the pad. It usually did this a couple of times a month, one pad was over the front of my hip joint, so close to parts essential and sensitive, and I mostly wore it at work, in an open plan office the size of a football pitch. Suddenly leaping out of my seat while shrieking like the blonde in a horror movie in front of a couple of hundred other engineers was so not my favourite thing.... (But pales in comparison to the battery incident).
It's a neuroconductivity test... they zap you at one end and time how long it takes the current to affect your muscles.
And just to make my life complete I probably should tell my GP we need to move ahead wth investigating the problem in my arm and neuroconductivity is precisely what she's proposing