Depending on the usage, the parent unit will work for up to 8 hours on a fully charged battery with power save turned ON. When the battery charge becomes low on the parent unit, the battery icon will turn red. At this point, you need to charge the parent unit. The rechargeable battery pack (supplied) can be charged and discharged hundreds of times, however it will eventually wear out and lose its ability to hold a full charge. When the in-use time becomes noticeably shorter than normal, it is time to purchase a new battery pack.