Battery lifetime will vary and is dependent on many factors including the amount of power drawn by the sensors and how long the interface is collecting data in the recording mode.
PASCO has done some tests where the SW500 interface was disconnected from the AC adapter to determine the battery lifetime. In sleep mode (no data collection), the batteries lasted approximately 48 hours. In continuous record mode, with minimum sensor load, the batteries lasted 9 hours. In continuous record mode, with higher sensor load, the batteries lasted 4.5 hours.
We recommend, when possible, that you use the AC adapter. You will need to plug the adapter into the outlet first and then plug the mini plug into the back of the SW500 interface. This process should increase the battery lifetime. If you are using the SW500 interface during data logging, be sure that the on/off switch on the back of the interface is always left in the on position.