The internal fan normally used to run during 120V charging comes on every 5-7 minutes or so, just for a second. The power is off, the AC mode is disabled, the fan just kicks on for a second then off. I’ve been watching the pack over the course of a couple days and it’s depleting it’s charge in doing this. Other people in the reviews have said the same thing, I ignored this when I decided to buy but will be returning it since the whole point of a battery pack is for it to have charge when I decide I need it.