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Packed behind the 5.5-inch screen and the plastic chassis is a 2600mAh battery. This makes it smaller than the likes of the Galaxy Note 4's 3220mAh and the iPhone 6 Plus' 2915mAh, although both of these have significantly more powerful screens.
In theory the lower resolution screen will provide less of a drain on the battery. Couple that with the more power efficient Snapdragon insides and it would seem that the smaller battery should be more than enough.
Throughout my testing I found that the battery inside the Desire 820 is more than enough to cope with day-to-day use, even with my heavy usage. I am also permanently connected to messaging apps, leaving Skype and Facebook signed in 24/7, as well as actively using a variety of other messaging services like WhatsApp and Snapchat.
I also have my Sony Smartwatch 2 connected via Bluetooth all day, and spend a lot of time moving in and out of patchy Wi-Fi and mobile data range. Screen brightness was left on automatic, as I found that the Desire 820's screen was bright enough, even out in daylight.
It should also be noted that I also had the vibration turned on, a feature that actually drains the battery more than having sound on. I did, however, have sleep mode turned on, which disables data when the phone isn't being used for long periods.
After 10.5 hours of use, the Desire 820 was down to 35%. This might seem a little low, but is a similar figure to what I have experienced on my own HTC One.
To compare with other handsets, during TechRadar's HD video battery test, a drop of 25% was noted. Other larger handsets also saw a similar drop, so the smaller battery isn't really a problem. The Galaxy Note 4 drop saw a 19% drop, with the iPhone 6 Plus scoring 27%, LG G3 at 25% and HTC One M8 at 23%).
For those looking to further their battery use HTC has included battery saving techniques. Power saving mode allows you to slow down the CPU, reduce screen brightness, turn of vibration and even put data to sleep automatically.
Extreme power saving mode takes it one step further, automatically engaging at a preset level; 20, 10 or 5%. In order for this mode to work, many functions of Android are shut down. In fact, only the phone, messaging, mail, calendar, calculator and clock are allowed to work. Even notifications are turned off.
Elsewhere HTC has thrown in some other battery saving techniques, such as its quick settings mode. Just like Samsung's toggles, these can be accessed through the notifications bar, although they are hidden on a second page.
A simple tap of the button in the top right, or swiping down with two fingers brings up the ability to toggle Wi-Fi, Bluetooth, data and screen brightness.
In short, HTC has done a lot of work to get the most out of the HTC Desire 820's battery, allowing a day's hard use without the need to carry a charger in your bag.
Messaging
Being an Android device means that a lot of the most basic messaging functions are well catered for. Email is handled with the two standard apps, apps that are both well designed and provide every function that you could wish for, including the support for aggregated inboxes.
Text messaging is handled with HTC's app, which is also well designed and fully featured, being far more attractive to use than the Samsung TouchWiz offering. Google's Hangouts app can also be used to manage your SMS messages should you desire.
As a HTC device, the Desire 820 does also come with a really rather superb keyboard. HTC has put a lot of effort in to ensure that its keyboard is amongst the best, matching some of the best third party keyboard apps.
A certain level of praise has to be attributed to the larger screen size, that 5.5-inch monster means that keys are larger and easier to hit. My initial concerns that the larger screen would make it difficult to type were unfounded, but will definitely affect those that like to type one handed.
Contacts and calling
Another of the most basic phone functions has to be the phone itself. Without the ability to make a decent phone call, the Desire 820 can't really be called a smartphone.
Thankfully I can report that phone functions are more than acceptable. Making calls is easy enough, navigating the contact list is swift, and smart dialling is also supported within the phone app. Within a call you can access the dial pad and speaker phone, although more advanced features are omitted.
Call quality is nothing special, although again more than acceptable, with the stereo speakers also providing that extra oomph when on loudspeaker. Signal holding was also really good, but still suffered in known black spots.
Internet
One area that the big screen is an advantage is while browsing the web; the larger screen size makes it easier to browse sites and is a godsend when it comes to browsing fully-fledged desktop sites.
Browsing the web can be done through one of two apps, either Google's own Chrome app or HTC's customised Android app. My preference has always been Chrome, however both apps handle the web in a very similar fashion.
Both offer tabbed browsing, both sign in to your Google account to draw down your bookmarks, both even offer incognito browsing so your wife won't find out that you're looking for her birthday present.
The biggest difference seems to be that the HTC app defaults to a home page where Chrome brings up a page showing the most visited pages.
Loading pages was handled swiftly, whether over 3G or Wi-Fi, and those that live in 4G enabled areas will be pleased to note that the Desire 820 is also 4G capable.
