Apple Watch not counting exercise minutes

I can't comment on what happens when the battery runs out - I'd assume it would record everything up to that point, but am not sure.

However, apart from that 'Outdoor Walk' causes a lot of confusion for a lot of people because of what qualifies as 'exercise'.

As far as the Apple Watch is concerned, a walk is only 'exercise' if you exceed a certain pace (about 18:20 minutes/mile, IIRC), or if your heart rate rises above a certain level.

This means that if you're taking a leisurely stroll, stop to talk to the neighbors, or are walking the dog who stops to sniff at every lamppost, fire hydrant and blade of grass on the way, you might not meet the criteria for 'exercise'.

Without knowing more about your walk it's impossible to be more precise, but these are some of the things that catch out a lot of people.

To earn 1 minute of exercise credit(green ring);

Travel a full minute at a brisk walking pace(3.3 mph approx) or above.

Raise your heart rate to approx 75% of your maximum.

When you're at around or above this heart rate for the entire minute you'll receive 1 exercise minute credit.

If you pause or slow down then you won't get any exercise credit.