The Xiaomi 11T & 11T Pro Review: Two Chips, With a Battery Focus

Q. - What does up to 800 cycles mean? What are the criteria for this figure? Usually there's always some specification such as "retain up to 80% charge after 800 cycles".

- How were the charging cycles tested? What was the depth of charge of the battery (from which percentage start of charge to which percentage stop of charge) - are these partial of full charge cycles? 

- How much more is the battery degraded compared to regular charging speeds? Does Xiaomi have any data to share in regards to battery health?

A. [...] The battery can obviously handle way more than just 800 cycles. You are absolutely right, the idea here is that it will maintain 80% of its capacity after 800 charging cycles, which is roughly two years before you'll notice any real difference. For most smartphones that number stands at only 500 cycles. The testing conditions are simple, we test the batteries under room temperature charging and discharging it thousands of times to make sure that the battery is able to retain most of its capacity.

In the initial PR a few weeks ago the 80% figure wasn’t mentioned, hence why I asked about the 800 cycles number.

In general, the issue we’ve been having with a lot of vendors is that we are having a lot of issue in getting anybody to actually specify the exact details of the test environment of these charge cycle tests and results.

In particular, I’m asking about the depth of charge of the test – a cycle can either be a full 0-100% charge, or it can also be 5 40-60% charges, in battery terminology, both of those count as a full cycle, however the 0-100% cycle will put significantly more stress and degrade the battery a lot more than the 5x 40-60% cycles.

Xiaomi here also isn’t very clear in their answer and didn’t address the question. Particularly, they talk about “most smartphones” only able to achieve 500 cycles, however, most smartphones don’t have 120W charging, so it can’t possibly be a valid comparison.

Xiaomi also notes that the battery is tested under “lab conditions” – this was also a topic of kerfuffle we’ve had with OPPO last year as the company kept producing questionable test results without any context of test methodology.

Usually, these battery stress tests are done via industrial battery charge/discharge capacity testers, meaning they are testing merely the battery cell, outside of the phone - a very important distinction compared to actual phone charge cycle stress testing.

Q Follow-up. - Can I get a clarification as whether this means that the batteries are being tested externally, outside of the phone, or if this means that the phone itself is being charged and discharged with the 120W system?.

I followed-up with the above question for clarification. This was also a stickling point with OPPO last year, as they would refuse to answer that the advertised charge cycles and capacity retention was actually tested with the advertised fast-charging system. I haven’t had a response from Xiaomi yet on the matter, however this was extremely close to the embargo time, I'll make sure to follow up if they do respond.

Q. For the TÜV certification - we've had similar claims from other OEMs, but the issue was that the certification doesn't have any public test methodology documented, nor are the exact results ever published. It is our understanding that this certification only essentially checks that the device doesn't result in any hazardous situation, but doesn't test things like battery health. Any more information is helpful."

A.Correct, the TÜV and other battery safety certifications are mainly focused on battery safety, and not on battery health.

However, at Xiaomi we use laboratory cycle verification, third-party laboratory tests, and ORT verification methods to ensure that the battery cycle life meets the highest standards.

Finally, I asked about clarification about the TÜV certifications. This was also a stress point in an interaction with OPPO last year, as they were trying to portray that the TÜV certification actually is testing battery degradation. Documents sent to me at the time were clear that they were completely unrelated to the fast-charge system.

Xiaomi deserves credit here to properly dismissing that notion and confirming that the TÜV certification is only related to safety – as in, they test that the charger or phone don’t blow up. Battery health and degradation is unrelated to the (non-public) test-procedures and certification.

Unfortunately, it’s been extremely hard to get a clear non-evasive answer from any vendors out there that promotes such extreme fast-charging systems. Xiaomi here also wasn’t able to produce any kind of convincing evidence that would argument that the 120W charging system doesn’t notably impact battery degradation.

We’re in the process of writing up a more dedicated and general fast-charging article that focuses on real data, and the actual latest science on fast charging. There is an incredible amount of misinformation, misconceptions, and outright falsehoods that are floating out there that we want to address.