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...

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...

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.