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I have a 620 with Amber. With Windows 8 it will last more than 2 days.
With Windows 8.1 it only lasts 6 hours. I have tested with Amber and Black and it's the same.
The phone keeps warm all the time and the battery drains fast.
I can't test Cyan because it's not available for the 620, but I am dubious about the battery duration.
No. It's a fresh install with DevPreview after that. There are some threads about it.Maybe your data is on and a lot of background apps are on??