A few months ago I had a rude surprise when I got up one morning… my several years old MacBook Pro was sitting at an angle. Upon inspection, the battery had peculiarly started to bulge out in the center. Over the proceeding several days it continued to bulge to the point that the battery didn’t work at all and my laptop was unusable with the battery installed due to the weird angle it perched at.

After a few weeks I finally went to the Apple store to get a replacement battery, since the laptop was old but still worked perfectly otherwise. The ever-helpful employee was kind enough to ask around and figure out what had happened…

Apparently back when my laptop was made Sony was the contracted company for battery production. As frequently publicized afterwards, Sony batteries had a tendency to… explode. Rather than replace all the batteries they already had, Apple designed a safety mechanism around the battery and encased the entire thing in a gel. If (and when) the battery then exploded, rather than spraying acid all over your desk and possibly igniting everything, it simply expanded and stopped working.