When must the battery in an emergency locator transmitter (ELT) be replaced (or recharged if the battery is rechargeable)?

• A. After one half of the battery's useful life
• B. After one quarter of the battery's useful life
• C. After the first year of service
• D. Only when the ELT is used in an emergency

Answer: (A)

ELTs rely on a power source that must be ready to perform at a high level when needed. The battery’s capacity degrades with time, even if the unit isn’t used, so to keep the transmitter可靠 in an emergency you replace or recharge the battery after halfway through its rated useful life. That halfway point ensures there’s still ample energy available to transmit for the required duration when an activation occurs. If the battery is rechargeable, you follow the same rule—recharge at that 50% point to restore the designed performance. Waiting for a calendar anniversary or for a full year, or only replacing after an emergency, could leave the ELT with insufficient power when it’s actually needed.