The batteries have been tested to last for some 9 to 20 hours of continuous use, depending on the type of batteries used. Mimio recommends using either rechargeable batteries or lithium batteries. While lithium batteries are one-time use and expensive, they will give you the longest use time. However, rechargeable batteries will provide multiple uses and ample time to be used, for multiple days in a row. Remember, the MimioTeach system will go to a low power state after 30 minutes of inactivity.