Performance, storage and stamina
The One M9 runs on a Qualcomm Snapdragon 810 octa-core processor along with 3GB of RAM. As has been the case with other recent HTC flagships, performance isn't something you'll have to worry about: The M9 is consistently smooth and snappy, and I've yet to experience even the slightest bit of lag anywhere in the system.
Some reports leading up to the M9's launch suggested heat might be a problem with this phone. I've felt the device get somewhat warm during especially intensive usage, but it's never been particularly bothersome or alarming.
Battery life on the M9 is best described as passable. With moderate use, the phone should be able to get you from morning to night most of the time -- but if you tend to use your device a lot during the day, you might see that dreaded "low power" warning before you reach bedtime. I've safely made it through most days with three to four hours of mixed-use screen-on time, but I've often cut it closer than I'd like. The One does not support wireless charging. And the phone's battery is not removable.
The M9 does support Quick Charge 2.0, which allows you to boost your phone's battery by as much as 60% with just half an hour of being plugged in. There's just one caveat: The charger HTC ships with the phone isn't Quick Charge-enabled, so if you want to take advantage of the accelerated charging, you'll have to buy your own Quick Charge accessory. You can find off-brand Qualcomm-certified chargers for as little as $15 on Amazon, but it's still pretty lame that HTC doesn't just give you one with a $650 phone.
How about storage? The M9 comes with 32GB of internal space, of which about 22GB is available to use after factoring in the operating system and various preinstalled applications. The phone also has a micro SD card slot that lets you add up to 2TB of additional space (theoretically, at least -- cards that large aren't yet readily available, but anything smaller will work as well). And on top of that, it comes with 100GB of cloud-based Google Drive storage for two years -- a $48 value.
Call quality on my T-Mobile-connected review unit has been fine: Voices are loud, clear and easy to understand, and those with whom I've spoken have reported no trouble hearing me. Data speeds over T-Mobile's LTE network have also been A-OK and in line with what I typically see from that network in my area.
Perhaps the biggest criticism of HTC's previous One devices revolved around the phones' cameras: While the UltraPixel system present in the past two flagship phones worked wonders when it came to capturing light, it was less versatile than other smartphone shooters, and its low resolution made images less flexible for editing.
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