Top up charge before bed, overnight the battery went from 75% to 58% seven hours later. So assume about 20% loss overnight, which is totally doable. What was funny was I woke up but didn't get up, just started reading in bed, until my watch nagged me to stand up after 50 mins. Didn't try haptic alarm to wake up yet. But the "can't be used for sleep tracking" is not true. Now the health app still sucks - just hangs when you try to click on full data, but surely that will change with time and development. You can see hourly highs/lows graph summary. And I can't find a way of accessing anything on the watch prior to current or last heartbeat. Will experiment with how the easiest way to charge is. I suspect 45 mins from waking up/breakfast and a top up at lunch or dinner will work. First full day starting now. If you have sleep issues, the Watch is useful for keeping an eye on overnight heart rate, with way less discomfort than a chest strap. (but only 10 minute sampling vs continuous) PS - Even though my phone was tracking my steps, the activity app only gave me credit for steps after the Watch arrived at lunchtime yesterday. (pics or it didn't happen said the Watch) iPhones are now second class citizens. New boy in town.