Miller was able to force the batteries to overcharge, and he considered the possibility of making them catch fire or explode—but decided he didn't want to destroy his home. Miller also told interviewers it might be possible to create malware that could be hidden in a laptop's battery, so it would return no matter how many times the attack code was removed from other components. But he didn't try to make that happen, either.
"You could put a whole hard drive in, re-install the software, flash the BIOS, and every time it would re-attack and screw you over. There would be no way to eradicate or detect it other than removing the battery," Miller speculated to Forbes.
That's true. But as Miller himself pointed out, there's also no way for the malware embedded in the battery to get out without the help of another piece of malware in the operating system or an application—one that would copy the battery's malware out of the firmware and into the laptop. A fresh install of a hard disk, operating system and BIOS wouldn't have any reason to include that type of code. It's an if-we-had-some-pastrami-we-could-make-sandwiches-if-we-had-some-bread scenario—interesting speculation and a real headline grabber, but not a realistic threat.
It's also unlikely that Miller would ever have been able to use firmware hacks to make a battery explode, thanks to the improved design of laptop batteries in the wake of actual incidents of batteries catching fire. The internal fuses that now prevent that type of massive overheating from happening accidentally also prevent it from happening intentionally. Evil firmware or not, when fuses blow, the battery will shut down. (At least one earlier researcher specifically tried to make lithium-ion laptop batteries catch fire using firmware. He never succeeded.)
But malware that shuts down a battery permanently? Completely, frighteningly plausible, and a threat that could disable millions of laptops at once—from Apple or possibly other manufacturers. Too bad the real danger is likely to be obscured by visions of explosions and unkillable viruses. Those might make great summer movies, but that's about as far as they're likely to go.