Hard Mac has been getting quite a few reports from Macbook owners of swelling batteries, the problem is dominant in Mac Book Pro 17".
I am the system administrator of a research lab and I have been facing the "swelling battery" issue. among 4 MacBook Pro 17" Core Duo ordered, three of them had swelling battery, and should be replaced.
The first sign of the problem that will lead latter on to the swelling syndrome is the random shunt-down of the notebook when running on battery. sometimes, it can also be identified by a lower reactivity of the trackpad, due to the pressure of the swelling battery.

Detailed reports are not available to give all serial numbers potentially affected, but it seems models ending with UUUS0A are particularly affected. Please note that such a battery can be exchanged for free and don't use it anymore as it potentially dangerous (explosion).
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