I find the battery on the HTC One is hugely impacted by the jiggery pokery Google do behind the scenes. I've had days where I've used 40% battery and days where I've not make it to the end of the day - same use, same conditions, it's really odd.
So, I think it has the capacity to have superb battery life, and mostly has good to very good battery life, but sometimes it can tank for no discernable reason, which I think is down to the activity of Google behind the scenes.
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