Redmi Note 17 Pro Max 5G: How did such a large battery fit into a phone less than 9 mm thick?

For many years, it was true that higher battery capacity meant a thicker phone. Just look at the so-called ultra-durable phones – even a few years ago, they could easily provide 20,000mAh capacity, but it came at the cost of insane weight. The Redmi Note 17 Pro Max 5G has “only” 9,210 mAh, yet you probably wouldn’t distinguish it from a regular mobile phone with a 5,000mAh cell. It seems like a technological miracle, but there’s one thing behind it all: silicon.

Why couldn’t batteries simply be made larger sooner?

I’ve essentially answered this question in the introduction. Regular smartphones are thin, and the battery occupies most of their interior. If a manufacturer had decided earlier to offer more milliamp-hours, the cell couldn’t be packed into the same space – they would have had to adapt the design, which would have impacted the device’s thickness.

Manufacturers therefore had to ask themselves how to get more energy while maintaining the same, or at least similar, battery dimensions. And the answer is precisely the use of a silicon-carbon mixture.

What is a silicon-carbon battery?

A silicon-carbon battery is still a lithium-ion battery; it differs from a conventional one only in its anode – the negative electrode where lithium ions are stored during charging. This was previously made from graphite, but now silicon is entering the game. Theoretically, silicon could accommodate many more lithium ions, but it swells and disintegrates during charging.

The solution is therefore to mix silicon with carbon, which holds it together. This reduces swelling from approximately 300% to 10–20%, which is manageable. The added silicon increases energy density by roughly 10–20% depending on its proportion, which simply means that more milliamp-hours can fit into a battery of the same size.

How does Redmi Note 17 Pro Max 5G utilize this?

As mentioned in the introduction, the new Redmi Note 17 Pro Max 5G features a 9,210 mAh battery. According to Xiaomi, the silicon content is 16%, an increase from 10% in the previous model. Thanks to the large battery, the phone promises up to three days of battery life on a single charge and 37 hours of continuous video playback.

Despite this, the phone is only 8.57 mm thick (or 8.65 mm, depending on the color variant) and its weight does not exceed the 230g mark. At 225 grams, it is one of the heavier phones in its category, but it is certainly not unacceptable. Even the Pixel 11 Pro XL weighs 226 g, and the iPhone 18 Pro Max weighs as much as 249 g.

The Redmi Note 17 Pro Max 5G battery can be charged with 100W power, and it also supports reverse charging with up to 27W for compatible devices, allowing you to wired charge your watch, headphones, or other accessories from the phone.

Silicon-carbon batteries also have their disadvantages

Despite the significant progress silicon-carbon batteries bring, they also have their general disadvantages. Compared to classic graphite cells, for example, they typically wear out faster, leading to a generally shorter lifespan. It’s not too surprising that their production is also more expensive.

Concerns about shorter lifespan are likely the main reason why more conservative manufacturers like Apple or Google are more cautious when it comes to using silicon-carbon batteries. Samsung is an exception, having implemented the technology in its latest foldables.

Xiaomi claims the new Redmi will tackle this. How?

However, Xiaomi assures that the Redmi Note 17 Pro Max battery will last long enough. The phone is equipped with a special Surge G2 chipset, which ensures higher safety, longevity, and reliable battery performance. As a result, it is expected to retain 80% of its original capacity after 1,000 charging cycles, which, according to the manufacturer, represents approximately a 6-year lifespan.

The company also highlights the TÜV SÜD five-star battery performance certification and promises stable performance at both high and low temperatures (reportedly tested in the laboratory at temperature cycles from -40 °C to 75 °C).

You can already buy the Redmi Note 17 Pro Max 5G

The Redmi Note 17 Pro Max 5G has a recommended price in the Czech Republic of 12,499 CZK for the 8/256GB configuration. The more expensive 8/512GB variant costs 14,299 CZK. The phone is immediately available from domestic retailers. Until October 18th, it can be purchased cheaper thanks to discount codes.

How big a role does battery life play in your phone selection?