THIS COMES WITH THE SONAR UNITE ONLY. IT DOES NOT HAVE A BATTERY. IT USES A CR-P2 6V BATTERY. THE ONLY ISSUE I SEE WITH THIS IS THERE IS WRITING ON THE BACK WITH SHARPIE (BATTERY IS REVERSED?) AND WHERE YOU OPEN IT UP TO PUT THE BATTERY, YOU CAN SEE IT HAS SOME DAMAGE. YOU NEED A SCREW DRIVER OR THIN COIN TO OPEN IT. THE PREVIOUS OWNER WAS TOO ROUGH ON IT BUT IT STILL OPENS UP FAIRLY EASILY.