The battery has the storage capacity to pass 510 mA in an hour. If you discharge at half the capacity (0.5C) it will be empty after 2 hours.
If it was to draw 51 mAh it would last 10 hours.
But if it would draw 1020 mAh it would only last 30 minutes
Naich@lemmings.world 16 hours ago
510mA per hour is nonsensical because A is an instantaneous measurement. 510 mAh/h is 510 mA. I guess you need a backpack to carry the battery around if you want the watch to last all day.