When the computer is on, the RTC (realtime clock) gets its power from the board, not from the battery. The chemical reaction inside the battery is stopped from proceeding by the potential at its terminals. In layman's terms: when the A3000 is on, the battery's charge is held inside it. When the A3000 is off, the battery has to keep the RTC running. Even when its past the point when it can't do that and keep the time any more, parasitic drain from the rest of the board will make it eat itself away. That's why you should never store batteries in anything that won't be used for a long time.
