Silicon-carbon batteries have made it possible for recent smartphones to launch with huge batteries, but many have been wondering why the tech hasn’t made its way to more smartphones, such as Samsung’s Galaxy lineup, Google Pixel devices, the iPhone, and others, and there are two key reasons for this.
The advantage of silicon-carbon batteries comes in energy density. This updated battery tech can store more power in a footprint the same size as existing lithium-ion batteries. This allows for slimmer phones to pack more power, while also expanding on what traditional form factors can already pack. Foldables are perhaps the best example we’ve seen to date, with devices such as Honor’s Magic V series and the Oppo Find N5 packing bigger batteries than even what we see in flagship-tier devices like the Galaxy S25 Ultra, despite their ultra-thin profiles.
So the obvious question has been, why aren’t these batteries standard across the board?
If they hold more energy in the same footprint, why not use them on every device so you can have bigger batteries in everything?
There are two reasons, it seems.
The first is regulatory matters. In the US, any device with a battery cell greater than 20Wh has to be labeled as a “dangerous good” in shipping and transportation. The calculation of this is broken down well by @UniverseIce, who shows that existing batteries are already getting pretty close to this limit. The Galaxy S25 Ultra’s 5,000 mAh battery hits 19.4Wh, where the 5,060 mAh battery in Pixel 9 Pro gets even closer at 19.68Wh.
If that’s the case, though, why are 10,000+ mAh power banks so abundant? That’s because this policy only applies to individual battery cells, not the total capacity of a device. As long as each cell falls under this 20Wh limit and the total capacity is under 100Wh, it falls under the exception for “smaller cells or batteries.” This is also how the OnePlus 13 with its 6,000 mAh battery falls under the exception, because its battery capacity is broken down into two cells.
That one big reason we’re not seeing these larger batteries in the US, as the headaches that would come with higher capacity may just not seem worth it to brands selling in the States.
But, arguably, there’s a bigger reason we’re not seeing silicon-carbon adoption en masse.
That reason is in the expansion of batteries as well as their overall lifespan.
A battery engineer speaking to David Imel (shared on the Waveform podcast) explained that silicon-carbon batteries age more quickly than traditional batteries, losing more capacity over their first 2-3 years compared to more broadly available battery tech. No specific numbers were shared there, but another supposed battery engineer adds that these batteries do indeed have a worse lifespan, and that is due to the expansion problem.
A pure silicone anode battery suffers from extreme expansion concerns. When charging, those batteries can grow massively in size over time — up to 400%, as one study from South Korea’s Gachon University found. In the fixed volume of a smartphone, that’s very obviously a problem. Silicon-carbon helps to solve this problem to some extent, but it doesn’t eliminate it entirely. A silicon-carbon battery can still grow more than a traditional battery over time, as that same study found, but it’s not quite as severe, coming in at around 3x growth as another study brings out (h/t SammyGuru).
This is a good reason to hold off on using these batteries, because that’s a significant problem to overcome.
Why are any phones using this tech at all? In the spec war, a big battery catches attention. That’s reason enough for some, but it’s not enough of a selling point for brands that are more wary of how their phones age or where they are sold. That’s why it seems software locks for silicon-carbon batteries are also happening with some devices. If you lock the battery to a point where it doesn’t charge to its full capacity, it lessens these problems.
The Nothing Phone (3) is our first really good example of this.
In most of the world, Nothing Phone (3) is marketed with a 5,150 mAh battery, but it has a 5,500 mAh battery in India. To be clear, Nothing Phone (3) does not use a different physical battery between its global and India-specific variants. The power pack is capable of 5,500 mAh capacity in all regions, but it’s marketed as 5,150 mAh everywhere else for the sake of leaving room for future expansion. Nothing told Mrwhosetheboss that if the battery is above a certain capacity in some countries, it gets labeled as a “dangerous good,” lining up with the regulation problem explained above. OnePlus previously did something similar on a Nord device, but gets around the regulation on devices such as OnePlus 13 (6,000 mAh) by using a dual-cell design.
Will these problems be fixed? Almost definitely. But, in the meantime, this is why you might not see silicon-carbon batteries in smartphones from other brands. And, frankly, Nothing’s example seems like a good one to follow. By limiting the battery by just a bit (around 6%), you’re getting a device that still has a full-size battery, but with an inherent cap that gives that battery a slightly longer lifespan just because it never reaches “full” capacity.
What do you think?
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