There is literally no way they could say "at least" with any number that would mean anything to anyone. Even if they did a range between worst case scenario (app refreshing as often as possible and running the CPU and Bluetooth radios 100%) to best case scenario (watch face that updates once per hour), would you really want to see a number that says "Between 5 minutes and 7 days of battery life!"?
You can't really even have a "under normal use" battery life claim. My Pebble lasts between 4-5 days depending on app usage. Other have theirs lasting 2-3 days. My personal iPhone sometimes needs to be recharged in the middle of the day. My work iPhone gets charged once every three days.
"Up to 7 days" is the most meaningful number they could put there, because it shows you what to expect while using it as a watch. Everything else is up to you.
You can't really even have a "under normal use" battery life claim. My Pebble lasts between 4-5 days depending on app usage. Other have theirs lasting 2-3 days. My personal iPhone sometimes needs to be recharged in the middle of the day. My work iPhone gets charged once every three days.
"Up to 7 days" is the most meaningful number they could put there, because it shows you what to expect while using it as a watch. Everything else is up to you.