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X-ray scans reveal the hidden risks of cheap batteries

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An X-ray image of an e-bike battery revealing its grouping of cells inside.

An e-bike battery featuring several smaller 18650 lithium-ion battery cells packed inside. | Image: Lumafield

Lumafield has released the results of a new study of lithium-ion batteries that “reveals an enormous gap in quality between brand-name batteries and low-cost cells” that are readily available through online stores including Amazon and Temu. The company used its computed tomography (CT) scanners, capable of peering inside objects in 3D using X-rays, to analyze over 1,000 lithium-ion batteries. It found dangerous manufacturing defects in low-cost and counterfeit batteries that could potentially lead to fires and explosions.

The study tested 18650 lithium-ion battery cells, which are used in various products including electric toothbrushes, power tools, e-bikes, power banks, and even electric cars. The batteries were purchased from ten different brands: three OEMs, including Samsung and Panasonic, sourced from “highly reviewed, specialized suppliers,” three vendors selling rewraps (typically OEM batteries with their plastic outer wrapping replaced) sourced from “specialized battery sites” or the brand’s own web stores, and four companies selling low-cost or counterfeit batteries sourced from “large, general online retailers such as Temu.”

A side-by-side comparison of two battery X-ray scans revealing issues with build quality.

Lumafield scanned 1,054 batteries – around 100 from each brand – and found 33 of them had a serious manufacturing defect known as negative anode overhang. The defect “significantly increases the risk of internal short-circuiting and battery fires” and can reduce the overall life of the battery,” according to Lumafield. All 33 of the batteries with the defects came from the 424 sold by low-cost brands or brands selling counterfeits. One of the counterfeits was identified by its pink wrapper designed to match the one Samsung uses on its 30Q cells. Other low-cost brands claimed capacities of 9,900 mAh while brand-name 18650 batteries have capacities in the range of 3,000-3,450 mAh. Not only were the counterfeits’ specs overinflated, but in real-world testing Lumafield found their capacities were less than 1,300 mAh.

When taking only low-cost/counterfeit batteries into consideration, there’s nearly an 8 percent chance they could have the dangerous negative anode overhang defect, based on Lumafield’s findings. For two of the counterfeit brands that were reporting impossible specs, the percentage of tested batteries from those brands that were found to have the defect were even higher – upwards of 12 and 15 percent. None of the name brand OEM batteries were found to have any problems, and while there was some deviation in anode overhang for rewrap batteries, the deviations were seven times worse for the low-end cells.

When looking at other indicators of build quality, all of the batteries from the low-cost brands also had much worse edge alignment of their internal wound layers than those made by reputable OEMs, increasing the risk of short circuits and performance loss.

Defects like negative anode overhang and bad edge alignment don’t mean an affected battery is guaranteed to explode or catch fire, but they can increase the risk of those incidents occurring, particularly when combined with other factors such as being left in a hot car or an accidental drop causing additional damage.

The results of Lumafield’s study suggest that batteries from reputable OEMs like Samsung, Panasonic, and Murata are safer and more reliable. And while rewrap batteries fared well in Lumafield’s test, their replaced wrapping makes it difficult to know exactly where they’ve been sourced which increases risks due to a potential lack of quality control in supply chain management. 

Not everyone has access to an X-ray CT machine to test the quality of the cells in every battery-powered device they purchase, but the study is a reminder that purchasing devices from reputable brands can increase the chances that their batteries are free of dangerous manufacturing defects. Trying to save money with less-known brands could end up costing you a lot more in the long run.

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Y Combinator launches “Early Decision” for students who want to graduate first, build later

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24 September 2025

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The accelerator has introduced a new application track called Early Decision, designed for students who want to start companies but don’t want to drop out.

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India court rejects X’s “free speech” argument, backs government takedown powers

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24 September 2025

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X sued the Indian government in March over content takedown orders issued through its centralized portal.

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The best Apple deals to shop ahead of Amazon’s fall Prime Day event

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24 September 2025

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The Apple Watch Ultra 2 is currently down to $649, matching its lowest price to date.

If the past is any indication, Prime Big Deal Days — Amazon’s upcoming fall Prime Day event — should deliver a wave of deals on Apple devices, letting you save on everything from AirPods and AirTags to the latest iPad. But if you can’t wait until the sale kicks off on October 7th to land a bargain, you don’t have to. A few Apple products are already receiving sizable discounts at Amazon and other retailers, giving you the chance to save ahead of Amazon’s two-day sales event next month.

Admittedly, the current discounts aren’t as steep as what we’ve seen during previous Prime Day events — and possibly this year’s October Prime Day — but they’re still a solid way to save on a lot of older Apple devices if you can’t wait. The last-gen Apple Watch Ultra 2 has returned to its all-time low, for instance, while the M1-powered MacBook Air is available at its best price to date. We’ve rounded up a handful of other Apple deals worth taking a look at below, so let’s dive in.

  1. The best wireless earbud and headphone deals
  2. The best iPad deals
  3. The best MacBook deals
  4. The best Apple Watch deals
  5. AirTags and other miscellaneous deals

The best wireless earbud and headphone deals

Apple AirPods Pro (second-gen) with USB-C charging case

The second-gen AirPods Pro improve upon Apple’s original pair with much better noise cancellation, improved sound quality, and onboard volume controls. The latest refresh also ships with a USB-C charging case, as opposed to Lightning. Read our review.
Apple’s second-generation AirPods Pro photographed on a reflective black surface.

Where to Buy:

  • You can buy a pair of the AirPods 4 on sale for $119 ($10 off) at Amazon, Walmart, and Staples. Apple’s entry-level wireless earbuds offer better sound than their predecessor, with richer bass and much clearer voice quality. The earbuds also feature an upgraded IP54 water and dust resistance rating, deep integration with iOS and other Apple products, and support for spatial audio with head tracking. Read our review.
  • Alternatively, you can buy the AirPods 4 with Active Noise Cancellation for around $169 ($10 off) at Amazon, Walmart, and Staples. Like the aforementioned base model, they deliver strong noise cancellation and a solid transparency mode, although they’re still not quite on par with Apple’s Pro models. The step-up ANC model also supports wireless charging and comes with a case that features a built-in speaker, making it easier to locate via Apple’s Find My network. Read our review.

Apple EarPods (USB-C)

Apple’s wired earbuds are comfortable, offer great microphone quality for the price, and feature a built-in remote for controlling audio playback.

Where to Buy:

  • You can buy the latest AirPods Max at Amazon and Best Buy in select colors starting at $499, which is a far cry from their all-time low of $399 but still a solid $50 discount. The plush over-ear headphones feature a luxe stainless steel and aluminum design, along with excellent active noise cancellation and an exceptionally natural-sounding transparency mode. They also support lossless audio, deliver up to 20 hours of playback on a single charge, and sport a USB-C port. Read our original review.

Beats Studio Buds

The Studio Buds feature support for iOS and Android as well as noise cancellation, a cozy fit, and good sound quality for the price. They don’t offer the same features as Apple’s iconic AirPods, but their broader compatibility may make them a fine choice on a budget. Read our review.

Where to Buy:

The best iPad deals

11-inch iPad Air M3

The latest 11-inch iPad Air features Apple’s fast M3 chip with GPU upgrades like dynamic caching for smoother performance in demanding apps. It also supports the Apple Pencil Pro and the newest Magic Keyboard, which features a larger build and a 14-key function row. Read our review.
A photo of an iPad Air on a table.

Where to Buy:

  • The 13-inch version of the M3-powered iPad Air with 128GB of storage is also on sale at Amazon, Best Buy, and Walmart, where you can buy it for an all-time low of around $649 ($150 off). Aside from a larger screen and better speakers, it’s identical to the aforementioned 11-inch model. Read our review.

13-inch iPad Pro M4

The newest iPad Pro comes in either an 11- or 13-inch configuration with Apple’s M4 processor. Both models also feature an OLED display, a much thinner and lighter build, new horizontal placement for the front camera, and support for the Apple Pencil Pro. Read our review.
A photo of a person pinching the screen on an iPad Pro.

Where to Buy:

  • You can buy the latest iPad with Wi-Fi and 128GB of storage at Amazon, Best Buy, and Walmart for $299 ($50 off), which is $20 shy of the tablet’s all-time low. It offers twice the base storage of its predecessor and faster performance thanks to the inclusion of Apple’s A16 Bionic chip; however, it still lags behind its higher-end siblings in performance and doesn’t support the newest Apple Pencil, nor does it support any of the AI-based Apple Intelligence features baked into the latest iterations of iPadOS. Read our review.

The best MacBook deals

2020 MacBook Air with M1 (256GB)

The 2020 MacBook Air has been discontinued but remains a great value. It comes outfitted with the company’s original M1 chip in one of three different colors (silver, space gray, and gold).
The MacBook Air is the most impressive laptop I’ve used in years

Where to Buy:

  • The 13-inch M4-powered MacBook Air is on sale at Amazon and Best Buy in all four colors starting at $799 ($200 off) with a 10-core CPU, an eight-core GPU, 16GB of RAM, and 256GB of storage. The fantastic laptop — which we consider to be the best option for most people — builds upon its predecessor with additional RAM and Apple’s faster, more powerful M4 chip. It can also connect to two external displays with the lid open, as opposed to just one. Read our review.
  • If you need more screen real estate, you can grab the latest 15-inch MacBook Air at Amazon and Best Buy with a 10-core CPU, a 10-core GPU, 16GB of RAM, and 256GB of storage starting at $999 ($200 off). It offers the same features as the 13-incher, but features an improved six-speaker sound system and your choice of either a 35W Dual USB‑C Port Compact Power Adapter or a 70W USB‑C Power Adapter.

The best Apple Watch deals

Apple Watch Ultra 2

The rugged Apple Watch Ultra 2 comes in one size: 49mm. It offers a large, bright display along with long battery life and excellent performance. It sports Apple’s last-gen S9 SiP, too, allowing you to take advantage of Apple’s double tap feature. Read our review.
The Apple Watch Ultra 2 on grass.

Where to Buy:

  • The last-gen Apple Watch Series 10 is on sale at Amazon and Walmart in the 42mm configuration with GPS starting at $329 ($70 off), which is $50 shy of its all-time low. While it lacks the Series 11’s more scratch-resistant glass and only lasts 18 hours, as opposed to 24, the wearable still delivers a bright, wide-angle OLED display along with depth and water-temperature sensors. It also includes FDA-cleared sleep apnea detection and supports Apple’s new hypertension notification feature. Read our review.

AirTags and other miscellaneous deals

Apple AirTag

Apple’s AirTag is unobtrusive, waterproof, and taps into the massive Find My network for out-of-range locating. Read our original review.
An AirTag in an Apple keychain accessory

Where to Buy:

  • The Apple Pencil Pro is down to $99 ($30 off) at Amazon, Walmart, and Target, which is $10 shy of its best price to date. Unlike Apple’s entry-level USB-C stylus, the Pro model charges wirelessly and offers other advanced capabilities, including Find My support, pressure sensitivity, and a “Barrel Roll” gyroscope that allows you to adjust the angle of your pen or brush strokes with a simple twist. However, compatibility is limited to the latest iPad Pro, iPad Mini, and M2- or M3-based iPad Air models.

Apple MagSafe Charger (2m)

Apple’s latest MagSafe charger now fully supports the Qi2.2 standard, allowing it to charge compatible devices (including the iPhone 17 series and Google’s Pixel 10 lineup) at 25W rates.

Where to Buy:

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