Silicon-Carbon Batteries Explained: Why Phones Now Last Longer

For years, most flagship phones were stuck at about 5,000 mAh. Then, almost suddenly, phones with 7,000 mAh batteries appeared without getting thicker. The reason is a change inside the battery called silicon-carbon. This guide explains how it works, why some phones sold in the US have been slow to adopt it, and why the mAh number alone does not tell you how long a phone will last.

What is a silicon-carbon battery?

A phone battery is a lithium-ion cell with two electrodes: a cathode and an anode. When you charge the phone, lithium ions move into the anode and are stored there. For decades, the anode has been made of graphite.

A silicon-carbon (Si-C) battery replaces part of that graphite with silicon. Silicon can hold far more lithium than graphite: about 3,579 mAh per gram, compared with 372 mAh per gram for graphite, roughly ten times as much. More lithium stored in the same space means a bigger battery in the same size phone.

Why phones do not use pure silicon

If silicon is ten times better, why not use only silicon? Because silicon swells by roughly 300% as it absorbs lithium, then shrinks again as it discharges. Over hundreds of charge cycles, that constant swelling cracks the material and wears the battery out quickly.

The solution is to mix a small amount of silicon into a carbon structure that cushions the swelling. The OnePlus 15, for example, uses about 15% silicon. That is why real-world gains are much smaller than the raw material numbers suggest: when Honor launched one of the first silicon-carbon phones in 2023, it claimed 12.8% higher energy density, and the actual capacity gain worked out to about 7%. Newer phones push the silicon share higher with each generation.

Which phones use silicon-carbon batteries?

Chinese brands adopted silicon-carbon first, and the technology is now reaching phones sold in the US, Canada and Australia:

Samsung confirmed its foldables use silicon-carbon to the press, but does not list it on its spec sheets. The Galaxy S26 Ultra keeps a 5,000 mAh battery and has not been reported as silicon-carbon. Apple and Google have not said whether any of their phones use it.

Note that OnePlus announced in July 2026 that it will no longer launch new products in North America, so the OnePlus 15 and 15R are its last phones for the US and Canada.

Why US phones lag behind

You may notice that the same phone sometimes has a smaller battery in the US or abroad, like the OnePlus 15R and Xiaomi 17 Ultra above. One likely reason is shipping rules.

US rules for shipping lithium batteries (49 CFR 173.185) allow simpler, cheaper shipping for cells up to 20 watt-hours and batteries up to 100 watt-hours. A 20 Wh cell works out to roughly 5,150 to 5,300 mAh, which is very close to the 5,000 mAh ceiling Samsung's Ultra phones have used since 2020. Larger cells can still be shipped, but as full dangerous goods with more paperwork and cost.

Splitting the battery into two cells, as the OnePlus 15 does, keeps each cell under the limit. No phone maker has publicly confirmed that shipping rules are the reason for their choices, but the pattern of smaller batteries in some regions fits.

mAh vs Wh: what the numbers mean

• mAh (milliamp-hours) measures charge. It is the number phone makers advertise.
• Wh (watt-hours) measures energy, which is what actually powers the phone. Wh = mAh x voltage / 1,000.

Because phone batteries run at similar voltages, mAh is a fair way to compare capacity. But capacity is only half of the story.

Why mAh does not predict battery life

How long a phone lasts depends as much on how efficiently it uses power as on how much it stores:

• The screen is usually the biggest drain. An LTPO screen that drops to 1Hz saves power when the image is still. See our guide to LTPO displays.
• The chip matters too. A more efficient processor does the same work with less energy. See our guide to 3nm and 2nm chips.
• Software tuning and the modem make a difference, especially on weak signals.

A good example: Google's Pixel 11 Pro XL has a smaller battery (5,115 mAh) than the Pixel 10 Pro XL, yet it lasted longer in published battery tests. Apple does not even advertise battery capacity; it rates iPhones in hours of video playback instead. For real comparisons, look at tests that run every phone through the same routine. Our guide to the best phones for battery life does exactly that.

Fast charging explained

Charging speeds are quoted in watts (W). A higher number charges faster, but only with a compatible charger:

• USB Power Delivery (PD) with PPS is the standard used by most Android phones, including Samsung. The Galaxy S26 Ultra charges at up to 60W wired with a PPS charger.
• MagSafe and Qi2 are the magnetic wireless charging standards. iPhones support up to 25W MagSafe and Qi2 charging. The Galaxy S26 Ultra supports 25W Qi2.2 wireless charging, but has no built-in magnets, so it needs a magnetic case for magnetic chargers.
• Proprietary charging from brands like OnePlus can be much faster, but often only with the brand's own adapter. In the US, the OnePlus 15R charges at about 55W because the adapter needed for 80W is not sold there.

Most phones no longer include a charger in the box, so check what charger you need to reach the advertised speed.

Does fast charging damage the battery?

Every lithium-ion battery slowly loses capacity as it is charged and discharged. Heat and spending long periods at 100% speed this up. Modern phones manage fast charging carefully, slowing down as the battery fills and as it warms up.

Phone makers now rate how long a battery lasts before it drops to 80% of its original capacity:

• Apple: iPhone 15 and newer are designed to keep 80% capacity after 1,000 charge cycles (older iPhones: 500).
• Google: Pixel 8a and newer are reported to be rated for 1,000 cycles.
• Samsung: EU energy labels for the Galaxy S26 series and Galaxy Z Fold 8 list 1,200 cycles, down from 2,000 on the Galaxy Z Fold 7.
• EU minimum: since June 2025, phones sold in the EU must keep at least 80% capacity after 800 cycles.

How to make your battery last longer

• Use a charge limit. iPhone 15 and newer let you cap charging between 80% and 100% in 5% steps. Samsung and Google offer similar battery protection settings.
• Avoid heat. Do not charge a phone under a pillow, in a hot car or while gaming for long periods.
• Do not worry about overnight charging. Adaptive charging features hold the battery at a lower level and finish just before you wake up.
• Use a good charger. A certified USB-C PD charger or Qi2 charger is safer and charges more consistently than cheap no-name adapters.

EU energy labels: a useful new number

Phones sold in the EU now carry an energy label with a rated battery endurance and the number of charge cycles to 80%. These figures come from a standard test, so they are useful for comparing phones even if you live in the US, Canada or Australia. For example, the iPhone Duo's label lists 4,883 mAh across two cells, an endurance rating of 51 hours 30 minutes and at least 1,000 cycles.

Frequently asked questions