Smartphone chargers are one of our most prized possession when it comes to tech these days. Some of us bring them out together on a daily basis, whereas some of us bring a power bank. One thing is for sure – these chargers differ from one another. For all smartphone reviews that we do, we highlight what type of charger the phone actually comes with, is it 5V 1A, 5V2A, or something else? Smartphone chargers do affect your user experience.

While we know that 5V 2A chargers can charge a smartphone faster than a 5V 1A charger. By simple maths, 5V 2A means 10W – that means double the speed of a 5V 1A charger, right? Unfortunately, that’s not the case.

While we here at Nasi Lemak Tech have been gathering battery charging curve data for quite some time, it was only until one day when it occurred to me to test the different chargers on a smartphone and see how it charges. From that curiosity, I dived into the rabbit hole that I can never come out of. We do have old chargers lying around the lab, too.

Since then, I have data for a handful of phones – the ASUS ZenFone 4, Huawei P20, Samsung Galaxy S9, and the Honor 9 Lite. Without further ado, let’s proceed with the experiment. We’re also going to change things up a little. As a scientist myself, we shall present the data in the standard scientific method.

This experiment was done independently and was not sponsored or paid by anyone or company.

Observation

Throughout the years of smartphone testing and using smartphones, I came across smartphones come with different chargers. Not just different brands, but different output currents. Some smartphones can charge faster than others despite having the same battery capacity.

There is actually a chain of question that I want answers to. Firstly, how does each charger’s output affect the time taken for the batteries to charge? Is it significant? How does the same charger differ from one smartphone to another smartphone?

Hypothesis

By general conscience, higher powered charger (in this context, higher output wattage) will yield faster charging, hence able to get to 100% faster. However, from past smartphone reviews here in at Nasi Lemak Tech, we found out that the charging speed will start to plateau starting from about 85% from its full capacity.

Apparatus/tools

For this experiment, we’ll be using a few different smartphone chargers. For the 5V 1A charger, I managed to find one from my trusty old Nexus 4. As for the 5V 2A charger, we’re using the one that was included in the ASUS ZenFone 4 that we reviewed here. We also used the Huawei SuperCharge that was included in the P20 in this test. The same situation applies to the Adaptive Fast Charger that came with the Galaxy S9.

As for the USB cables, we used the one that was included in the box with each respective smartphone.

Testing methodology

Sequentially, this is what we did:

The smartphone’s battery was drained to below 15%, cooled down to ambient temperature, cleared all suspended apps and restarted. The battery percentage logging app was set to log once per minute and initiated charging with 5V 1A charger. Cables that are included with the respective smartphone were used. After the battery reaches 100%, the log was saved. Step 1 and 2 were repeated with 5V 2A charger. As for Samsung Galaxy S9, the experiment was repeated with the Adaptive Fast charger. The experiment was also repeated for the Huawei P20 with the Huawei SuperCharge charger. Once all the results were gathered, the time taken to charge from 15% to 100% was taken from each data set.

Results

When all of the data was gathered, I can see an obvious, general trend that everyone knows – 5V 2A chargers charge faster than 5V 1A chargers. Everyone knew that, of course. Here’s the graph of all the charging curves gathered into one big graph.

When charging at higher speeds, the charging curve tends to plateau when it reaches around the 85% mark. We will explain more in the discussion section down below.

Discussion

5V 1A vs. 5V 2A

When we narrowed down to compare only 5V 1A chargers, we found out that the charging curve isn’t exactly linear for all smartphones. While they’re all using the same 5V 1A charger, the Huawei P20 has an apparent non-linearity in its charging curve. The P20 has a larger battery and charges faster compared to the ASUS Zenfone 4. This might happen due to the fact that the Huawei P20 has a better power delivery circuit and/or better battery design. The Honor 9 Lite and Samsung Galaxy S9 have similar charging curves.

Looking at the second graph where we compared 5V 2A charger on all of the smartphones we have, we can see that the Honor 9 Lite and the Huawei P20 are trading blows in terms of charging speed. They’re both very similar, but ultimately, the Huawei P20 manages to charge to 100% faster than the Honor 9 Lite. The ASUS ZenFone 4 improved a lot in terms of its charging speed, whereas the Samsung Galaxy S9 took first place in the race with 5V 2A chargers.

Fast charging?

Next, we separated both the Huawei P20 and Samsung Galaxy S9 into two independent graphs.

We can see that the Huawei P20 has a huge leap in terms of charging speed. Both 5V 1A and 5V 2A chargers have quite a linear charging curve, but bends like the perimeter of a quarter circle with its insanely high-powered SuperCharge. It plateaus aggressively around the 85% mark.

As for the Samsung Galaxy S9, the Adaptive Fast Charger performs better throughout the entire charging period compared to the 5V 2A charger, but not by a significant amount. However, either the Adaptive Fast Charger or 5V 2A charger is better than the significantly inferior 5V 1A charger.

Non-linear charging curves

Regarding the charging speed slowing down at around the 75%~85% mark, we have to look at how lithium battery works. Smartphone chargers start slowing down to protect the battery. From what we can see when we first talked about how 3,000mAh batteries last longer with FinFET, we mentioned that battery voltages varied between 3.8V to 3.85V. However, their charging voltages vary between 4.35V to 4.4V. From what we can find out, the charging voltage decreases starting around 75%~85% mark.

Different batteries have different rated voltages and different limited charge voltages – and it all boils down to battery design that dictates the charging speed.

Huawei’s SuperCharge works in quite a brute force manner. Firstly, the phone will need to determine what’s the battery level first. Assuming it’s like our case – at 15% when plugged in, it will receive the full 4.5A. Again due to battery safety issues, it will drop to a lower amperage – say about 2A when it reaches 75%. After that, the current drops even lower as the battery completes its charging.

That also explains why it takes a long time to charge from 90% to 100% between all phones and all chargers that we’ve tested.

Conclusion

In conclusion, here are a few key takeaway points in this study.

The charging speed slows down starting around 85% mark to protect the battery. This is an inherent trait for lithium batteries. Even for 5V 1A chargers, this trend can be seen.

5V 1A smartphone chargers should be obsolete by now. It’s inferior in all of our test cases.

5V 2A are the most common smartphone charger these days. It yields a great improvement over 5V 1A chargers. However, the charging speed is not doubled.

doubled. Despite having the same battery capacity for both the Honor 9 Lite and ASUS ZenFone 4, the charging speed differs significantly even when the same charger is used.

The battery used decides the charging curve and the time it takes to reach certain percentage of battery level.

We hope that you learned something regarding how smartphone chargers affect your charging time too. We know many users have multiple power banks and chargers at home and experienced different charging speeds while using them, but never knew why. Well, now you do.

We just have some fun here while learning something new, hence the typical lab report structure with the scientific method as our way of presenting these data. Added with a hint of nasi lemak, of course.

Share this out with your friends and family so that they learn more about their smartphone chargers too. If you have any questions, feedback, or would like to suggest the next experiment to do, let us know down in the comments section below or at our Facebook Page.

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