No polling is necessary. There are two unrelated issues.
The first issue is that refresh is broken in the built-in Ring Extender v2 driver. The fix for this is to switch to Denny Page’s (@dennypage’s) driver.
The second issue is that, when a power fail occurs and the hub shuts down, and then later reboots when power returns, the Ring Extender switches from battery to mains before the hub has rebooted, causing the “switch to mains” event to be missed (discarded), so the Ring Extender’s power source state in the driver still indicates that power source is “battery”. The fix for this is to have a Rule triggered on the systemStart location event, and have an action in that rule do a refresh on the Ring Extender. No polling is needed, just that single refresh when the hub boots.
