[G3 General] engmia:
Glad you noticed that yourself! Greenify was originally developed a few years back, and was useful in some scenarios (but not a magic-in-an-app solution). Quite a few Android versions have came out since then which have drastically changed the ways the operating system handles apps in the background. As such many developers have stated, that using Greenify shouldn't have any effect and in fact might be counterproductive (increasing battery as you noticed).

This is because Greenify is killing apps running in the background and your RAM usage just sits there, powered on, but empty (for example only 1 GB of your RAM is taken instead of 1.7GBs). As such, every time you start the app, it loads again, actually taking up more processing power (and as a result more power) from the device.

Greenify nowadays is only useful for "rogue" apps (badly written apps or apps that are doing things in the background that they shouldn't be doing) but you shouldn't have such apps installed on your phone in the first place! It still lives on as a legend and a myth though.

I also mentioned kernel tweaks in my previous post and your personal experience as you see confirms it. Unless you have an inheritent problem in the kernel, they aren't really offering much benefits. Installing a custom kernel (very similar to installing a custom ROM) usually just gives you more control over what you can do with the kernel or the settings it's using.

However to people who aren't proficient, aren't willing to read through documentations, perform constant tests and benchmarks on their devices, it provides not much use really. Do NOT mess with kernels if you don't want to be doing all of the above stuff, just stick to the stock solution (again, unless it has an inheritent problem).

As for your wakelocks, they sound quite normal, unless you have radio scanning features left enabled on your phone.

And then we move onto your colleague's 7 hours of screen time. I find that extremely doubtful, although not impossible.

Overall battery life depends on a lot of things: installed apps, screen brightness, radios, GPS, bluetooth, settings on the device, number of syncying services, streaming, what are you using the device for (watching videos, streaming music, streaming YouTube, playing games all have varying different tolls on your processing power, and thus power drawn from the battery) among other things, all affect the battery life you are going to get.

So even if you get the same phone as your colleague, you might get a completely different battery life out of the device due to the way you personally use it. This is multiplied by the fact how much multifunctional smartphones are nowadays (million apps in the app stores, doing a ton of stuff like navigation and basically 100 devices in 1) and not a one trick pony that only does one task and behaves the same in everyone's hands, unless the user is doing something wrong. Note: I am using "one trick pony" to describe the type of device I'm talking about, e.g. those old telephones with dials that we used to have that only can handle calls, and not imply that such a device is bad. Normally devices specifically designed to a certain task that are engineered well don't leave a chance to multi use devices (example: a dedicated photographer's camera will bring you a much greater image quality than the newest smartphone that claims they have the best camera in a mobile device).

And to delve even deeper, another thing that matters a lot for the battery device is the hardware inside (although not the screen in this case). The Snapdragon 801, albeit powerful, has it's problems and it's not the most power efficient chip. However that's why I noted in my previous post, that all modern rechargeable electronic devices use lipo batteries (phones, cameras, cars, you name it -- lipo is the king and only contender around).

The hardware that's put inside a phone is very important part of the battery life you are going to get. If you have two devices, which both have a 3000 mah LiPO battery inside, and one is powering a SoC 801, and the other a low end chip designed to be power conserving, you are obviously going to get a much better performance out of the power conserving chip, however at the cost of performance. You might still have a good enough performance for the tasks you need, but it's a balancing game done by both the manufacturer and the user.

Another example of this is laptops -- that's why you see some laptop batteries last 8 hours of web browsing time. You don't see any lag while web browsing since the power conserving chip has enough horsepower to handle the tasks that are thrown at it. However, try to boot up a modern game, and you're going to have a bad time.

And my high performance grade laptop only lasts 2 to 3 (if I'm very lucky) hours of web browsing. Because the hardware in it, is much more powerful, and consuming more power from the battery. Albeit I'm performing the same tasks, I would get a much better battery life on a power conserving chip. But on the other side I have no issues running games.

So again, it's a careful balancing game between the hardware and how are you going to use your device. There is no magic involved, and no company currently has some better battery technology that others haven't managed to recreate. If you give that company who made the 8-10 hours web browsing laptop, and ask it to put high performing hardware inside, it wouldn't come up with a magical number much different than the industry standard for that hardware.

And of course, there are differences between specific devices, batteries and etc! Just not that major..

Just look at 18650 batteries for examples (lipo's in another form): All the major brands that produce those batteries -- LG, Sony, Samsung and Panasonic have more or less the same capacity with difference varying by only a few percents. Then you see old rewraped laptop batteries *****FIRE brand, which claim twice the battery power of said brands, but are utter bul****. In benchmark tests they obviously perform worse than the "legit" batteries"