Indeed, according to the article, it could be bidirectional:
>Using that password, Miller said that he has been able to do almost anything from giving false readings to the charger and the OS to ruin the device, to completely rewriting the firmware.
I don't know if it would be possible to make the battery burst into flame or explode. After the Sony battery fiasco, I'd expect there to be some kind of hardware interlock preventing short-circuits. However, it is possible to overwrite the battery firmware to prevent the battery from being charged, thus turning your Macbook Pro into a very small form-factor desktop.
I had an internship at a company that made lithium battery packs. The control boards on the packs have primary cell protection provided by a specialized micro controller that monitors cell voltages and prevents over/under charge levels and monitors current, however they also have secondary protection ICs that are hardware based that will shut down the pack should the cells reach dangerously high levels, as well as fuses to prevent dangerous levels of current.
Net result, changing battery firmware can reduce usefulness of battery (higher charging degrades cell life, blow fuses etc) but the packs should have hardware based protection from being a safety hazard
Actually, Macbooks use lithium polymer batteries which are highly explosive when overcharged (http://www.youtube.com/watch?v=0MiM2E6pvfg). So by telling the OS that a battery is not charged when it really is can cause it to explode.
That's a bare LiPo cell wired directly to current— not a good demonstration of how a well-designed battery pack would behave, even one with malicious firmware.
>Using that password, Miller said that he has been able to do almost anything from giving false readings to the charger and the OS to ruin the device, to completely rewriting the firmware.
I don't know if it would be possible to make the battery burst into flame or explode. After the Sony battery fiasco, I'd expect there to be some kind of hardware interlock preventing short-circuits. However, it is possible to overwrite the battery firmware to prevent the battery from being charged, thus turning your Macbook Pro into a very small form-factor desktop.