Batteries -good?

Yesterday I checked the battery health via the app of all the radiators and they all reported as good. Today one of them needs replacing . Considering when I tested them after taking them out they were 1.38v instead of 1.5v is this really enough of a drop to warrant a change? And what is the point of the battery indication saying good? Surely it should say degraded or something if the battery is on the way out?