The majority of the ones we're looking at today come with an AC adaptor, which is suggested for powering the receiver and display. Most of them offer battery storage space in case you need to relocate the weather station without losing the data it has gathered.  This can be a problem with an RV since, unless you have solar panels, you won't have power everywhere you drive. You can purchase a station that turns off the display while on batteries and needs to be engaged with to brighten up, or you can look into solar panels or an inverter and then plug it in on occasion to change the batteries. The features of the weather station you're evaluating will determine whether it can function on battery power for months or not.