I love this watch, but I do find it confusing. I've fully charged it and it has shown nearly 3 days of battery life on occasion. Then like this morning fully charged and under two days' life. How can it fluctuate like that, without BT or the WiFi on? The watch is running normally according to the diagnostics. Can someone explain, there doesn't seem to be any consistency at all. All background apps have been closed down and the cache cleared.