Because the battery of the ICD is sealed within the main box of the ICD, that entire box must be replaced when the battery is low. Most modern ICDs use lithium batteries that need to be replaced every four to seven years, depending on how often an electric shock is discharged.

ICD batteries will not run out unexpectedly. When a battery is running low, the elective replacement indicator (ERI) is activated. Physicians can detect this activation during a routine office visit or during a telephone check (transtelephonic monitoring). ICDs will continue to function for approximately six months after the ERI is activated, allowing ample time to schedule an elective replacement procedure.

Aside from the ERI, changes may occur in the way the ICD operates that will indicate to a physician that the battery is beginning to run low. Patients may or may not be able to feel these changes in function. Regular communication with one’s physician is an important part of a successful experience with an ICD.