Many people get tired of having to charge rechargeables. Even if they are happy with the vibes, they generally want to go back to a plug-in when they can.
The best would be one that vibes harder when plugged in, but can be unplugged and used for a good 25min, minimum, sesh... And also be water resistant.
That way I you can run plugged unless for some reason you don't want the cord or the danger of using it plugged in near water.
