I found the same thing: the rule triggers when any value changes and any of the values is less than the specified trigger (even if the device that generated an event has a value that is not in this range):
I remember "any" triggers working like this a while back and thought that was considered a bug, since fixed, so perhaps it was inadvertently re-introduced. I downgraded to 2.3.0 and verified that this behavior was different, as I remembered (and as you mentioned).
You might also try Device Activity Check which can simply let you know when a device battery dies and it goes offline. I use this for all my battery devices. I gave up on battery level notifications, because many of my devices hang at 1% or 0% for WEEKS before they completely die, and as a result I was changing batteries much more often than I needed to change them.
The flaw with this approach is that sometimes it's critical when a device dies. For example we recently took a very long road trip. One of the most important types of devices NOT to die while you're gone is water sensors. I would rather replace the battery a little early than have them die a day after we leave for an extended trip. I turn off the water, but still, stuff can happen. Like sump pump failure or water heater leaks.
I'm pretty sure they have always worked this way. Call it a 'feature'. The logic is as follows: If any of these devices send an event, see if the condition that any of them are in the target state or not is true. That's different obviously than seeing if the eventing device is in the target state. However, this sort of trigger uses the same logic as a condition of any being below a threshold. This would not be something easy to change.
So, if what you want is to trigger only if the reporting device is less than a threshold, use separate triggers, one for each device -- not a multi-device trigger.
Well, it did change after this last release. Until I updated, I only got a single alert for my dying water sensor. I watched it for 26 days while I was on a road trip. Once I updated 2.3.1.x upon my return, I starting getting all of these random notifications. All is well as I have changed to another method to watch batteries.