I recently flagged a potential issue with battery usage in the new Apple Watch, in this article. I have now had a chance to investigate this more thoroughly, and here provide my results and conclusions.

There are four different conventional positions in which you can wear a watch: on the left or right wrist, and with the face on the outer/upper surface of the wrist, or on the inner/lower surface. I suspect that the most common positions are on the outer/upper surface, but some of us (me included) have taken to wearing our watches on the inner/lower surface where they are less prone to physical damage, and sometimes more convenient to use.

It appears that, for the moment, you should only wear an Apple Watch on the more common outer/upper surface.

If you wear one on the inner/lower surface, then you are likely to experience problems activating the watch deliberately, and a high rate of unintentional activations which will significantly shorten its battery life (that is, the duration which it will operate before requiring charging).

These adverse effects can be made worse by everyday activities such as cycling.

I have measured the rate of discharge of the battery in my Apple Watch 1.0 (software 1.0) steel with Milanese Loop, as follows. Rates of discharge are given as fall in indicated percentage charge per hour, starting from 100% (fully charged).

Over 150 minutes of wear on the inner/lower surface of the right wrist, including 10 minutes brisk road cycling, with no intentional activations, rate of discharge = 3.6 % per hour;
over 155 minutes of wear on the outer/upper surface of the right wrist, including the same cycling, with 2 activations to respond to notifications, rate of discharge = 0.4 % per hour.

The percentage charge scale is unlikely to be truly linear, particularly at the extreme ends of its scale, but I believe these measurements to be comparable.

Estimated rates of discharge ranged between 0.4 and 4 % per hour, depending on Watch use. However even at the high rate of 4 % per hour, a full charge should last at least 17 hours before hitting the ‘red’ at 30% charge remaining.

As someone who does occasionally have waking days which reach or exceed 20 hours, I do not think that such days would cause a problem for watch usage. However what has become apparent is that the Watch needs rather more time to charge than I sometimes sleep: when only charged for just over 6 hours, it was not starting the day at 100% (even though I was!).

My take-home lessons are therefore:

1. Wear your Apple Watch on the outer/upper surface of your preferred wrist.
2. Don’t worry too much about its battery life: it will cope well with extensive use.
3. However it is likely to need at least 7 hours of charging in the night to get back to full charge for the morning.
4. Your mileage may vary of course, in which case you may need to gain better insight into your own use, etc.