how long does a charge last on the series 3 Apple Watch?

60% sounds about right for me too. The 18 hour quoted figure is for a fairly brutal standard test cycle of intensive use, most regular users would probably find it difficult to fit it around their employment and domestic commitments.

I just returned mine. Very unhappy with its operation.

The official answer is 18 hours but, in my case, I typically have 60% remaining at the end of the day.