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.