It uses 1 AAA battery.
I'm not sure how long it lasts..I've yet to replace mine after a month (use it everyday). Hopefully, I won't have to replace it for a while - although a few times a year isn't bad at all.
It's also shower safe
The first few times I used it, I didn't like it.
I thought the pulsating action was very subtle before I bought it. Instead, as someone pointed out, it feels very much like a vibartor...or, um, cellphone ringing against your face...
But you get used to it and it actually does seem to shave closer, with less effort.