It doesn't seem like cruel luck to me. More likely a sign of a common issue in the electrical systems that also contributed to the APU battery fires. If the emergency locator beacon is connected to the main electrical system as well as having its own battery power (as I would expect) then it wouldn't seem impossible for wiring issues (e.g., power surges) to play a role. I don't find this news reassuring at all. A non-electrical fire would have been reassuring.