>They are probably some kind of interface. The batteries in most
>"packaged" type packs have a monitoring and control chip in them
>that takes care of balancing and such like.

It hangs on the SMBus AIUI (an 'enhanced?'version of I2C) and keeps track of 
things like state of charge (this is where the laptop gets its % charge 
figure from) and stops the battery getting over discharged. 

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