Screen on time and Battery performance

For a while now, the terms Screen on time and battery performance have been used together in the same sentence. This is usually when smartphone users talk about how long their phones can last on a single charge or how well their batteries perform.

Manufacturers use it in adverts too to describe how long a battery should last on their new smartphone. Reviewers and marketers have turned it into a potent marketing tool to persuade or dissuade buyers on their next phone purchase.

Having said all these, what is the relationship between Screen on time and battery performance?

Screen-on-time (or SoT) means the length of time that a screen is on from a full charge down to less than 10% of battery. Battery performance (or endurance) can be loosely described as how well (or how long) a battery can hold a charge.


READ: What is SoT?


A lot of people tend judge the battery performance of their phones on screen on time. Manufacturers encourage this by touting SoTs in their adverts and baking it into their software. Reviewers and Marketers too keep up the trend and now the average consumer uses it as a metric to judge any battery related performance.

All one has to do is claim that their battery is impressive and he/she would be bombarded from all angles with requests of SoT screenshots for proof. SoT is without doubt the standard metric for judging the performance of batteries worldwide.

Now here is an opposing point of view.

What if we were all wrong? What if SoT was inadequate for judging the full performance of the battery of a smartphone?

Why SoT is not a good judge of battery performance

SoT as the name implies only SHOWS HOW LONG a screen was on. Keeping a screen on is only one facet of the very many tasks that your phone has to perform. Most of these tasks are performed with the SCREEN OFF or in the background. These tasks consume battery too.

As a telecommunications device, your phone has modems for mobile broadband networks/internet, Wi-Fi and Bluetooth. These modems if turned on, are going to be actively working in the background. They are either searching for networks/device connections or keeping you connected.

Poor network reception or using your device as a modem takes a huge toll on battery life which will then impact SoT negatively. This is because during bad network, the Operating System (OS) has to push more battery power to the modems to boost or keep your network connection stable. This is done even when the screen is off or in the background.


Read: How to check signal strength on your smartphone


The type of SoC (processor) used also affects SoT too. Using a 32nm or 28nm processor will drain your battery pretty quickly. It is partly in order to boost battery life that manufacturers are cutting down on the size of SoC transistor sizes. The smallest around is 5nm but TSMC is currently pushing for 3nm soon.

Certain processes e.g. for fingerprint scanners or ambient light sensors, are always running in the background and never go to sleep. These are in the background, consuming battery even while the screen is off.

Screen brightness level, size, resolution or type (LCD or OLED/AMOLED) also determines how long a battery would last. OLED/AMOLED should get better SoTs than LCDs. The lower your screen brightness and resolution, the longer your battery should last and vice versa.


Read: Screen size vs Screen resolution


There are also apps that run in the background like Google Playstore, Facebook and WhatsApp. These apps are constantly working even with the screen off and drain battery while they are at it. While we are still on the topic, there is a task manager on your OS that manages all background apps and processes and it also requires battery to run.

App use too goes a long way. Playing games is a sure way to run down your SoT while using your phone sparingly is a good way to boost it.

Also note that weather conditions especially temperature levels, can affect your SoT. On a hot day, your SoT should take a hit because heat and SoCs are not friends.

Putting all of these together means that even on the same type of battery, no two persons can get the same SoT. Even one person cannot get the same SoT twice unless they faithfully maintain the same usage pattern.

SoT readings can be wildly skewed and irregular and thus makes it a bad metric standard for either comparing batteries or judging battery performance.

There is a myth that if a battery is of a certain capacity, then there should be a benchmark of SOT it should deliver. For example, a 4000mAh battery should give up to 8hrs+ of SoT. This is not true. SoTs can vary wildly depending on one or all of the aforementioned factors. Smaller batteries may even get better SoTs than bigger batteries sometimes.

Now while SoT doesn’t show the full picture of a battery’s full performance, it is not without it’s merits. SoT should not be completely written off but should be used sparingly and cautiously. Note that it is not the final arbiter of battery performance. So this means that one bad SoT reading is not the end of the world. You could get a better SoT tomorrow based on the circumstances that the phone could be used in.


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