MacBook Pro Battery bulging after 10.6.8 upgrade

Question

I have a MacBook Pro Core Duo 17-inch: 2.16GHz (MA092LL/A), purchased in May 2006. It has been a superb performer. I ran Tiger (10.4.11) on the machine until recently, when I upgraded to Snow Leopard (10.6.8). I usually run the machine on the power supply, but the battery has never had any problems. I had the full 3-year AppleCare warranty on the machine, but obviously that has expired.
Today I noticed that the battery (A1189) was bulging. I hadn't used the machine for several days. I've probably used it for a total of 4 hours since I installed 10.6.8...and all of that usage was with the power supply connected.
I removed the battery and inspected it. The cover plate (with the battery check switch and LEDs) was separating from the body, obviously being pushed up by expanding innards. All 5 LEDs lit up when I pressed the battery check switch, so I replaced the battery and booted the machine (power supply attached). The battery indicator in the menu bar showed that the battery had 100% charge. I usually run the machine with an external Apple keyboard and mouse. Within a few minutes I was unable to use the mouse. The pressure from the expanding battery was locking the trackpad button and disabling all mouse click functions.
I released the battery locks; it wasn't easy due to the pressure caused by the bulging battery. That relieved the pressure on the trackpad, after which the mouse (and trackpad button) worked normally.
Unfortunately, I can't check the battery info in System Profiler; installing the battery locks the trackpad button and disables all mouse functions. However, my usage of the machine has been light, and I've mostly run it with the power supply attached. I have deliberately run the battery down to zero to calibrate it a few times per Apple's instructions, but since the vast majority of my usage has been on the power supply, battery performance has never been an issue. In the few dozen times when I've run the machine on battery power, it worked fine. I would estimate that the battery has used significantly less than half of its available charge cycles. It's obviously still holding a charge.
I've seen a number of posts here in Apple Discussions implying that Snow Leopard 10.6.8 might be causing some problems with MacBook Pro batteries. All my software is up to date. I understand that batteries don't last forever, but the fact that the battery is self-destructing within a few usage hours after I upgraded to 10.6.8 causes me to suspect that this isn't just a battery problem. I don't want to replace the battery and have it self-destruct again if there's a system power management problem.
Can anyone provide any suggestions or information on this issue?
Thanks!

Answer 1

stevekn:
After the same thing happened to me, I spent a great deal of time researching this issue. When I wrote the original post in this thread, I was asking whether there was a causal link between my upgrade to OS X 10.6.8 and the bulging battery problem. From the standpoint of the system itself and its ability to manage the battery functions, I'm now convinced that no such problem exists. Similarly, I'm convinced that there is no intrinsic defect in the battery itself...well, except to the extent that I'm about to describe.
All batteries have physical limitations. Among them, operating temperature is perhaps one of the most critical. It's no secret that what used to be called "laptops" are now called "notebook computers" because they get so hot during usage that you can't hold them on your lap—especially when the CPU is working hard for extended time periods. Applied to the MacBook Pro, that means one of the most stressful usage modes for its battery is the condition wherein the machine runs hot for a long time.
My MacBook Pro experienced exactly that  condition during my recent system upgrade, in which I had to install Leopard as an intermediate step in order to be able to install Snow Leopard. I suspect that it was the Leopard install that dealt the death blow to the battery. It required lots of CPU usage for a long time, and the battery got very hot in the process. (Of course, it was running on the power supply at the time—which is advisable for a system upgrade.)
During the Leopard install, I checked the machine. That's when I discovered how hot the the machine had become. I had never observed the MacBook Pro getting that hot during any previous usage. I put a couple of heat sinks under it and elevated the machine, but I now believe that by then it was too late.
It's my opinion that the battery simply couldn't tolerate that kind of heat. Shortly thereafter, the two center cells started growing, with the resultant trackpad symptom revealing the problem...and by now you probably know what happens after that. The bulging indicates internal damage to the cells, in which the chemical compounds interact in such a way that causes the cells to expand.
In the case of my battery, I had set it aside and then had forgotten about it while I researched a replacement battery. When I found the damaged battery several weeks later, it no longer looked like the battery in your photos, with some separation of the battery case and cover. I discovered that the damaged cells had continued to expand slowly in the interim, eventually forcing the battery case completely apart. I suspect that if you observe your damaged battery over time, you'll find that the damaged cells continue to expand in the same way.
That's typical behavior for damaged cells, so in that sense, it's "normal". Whether it's "normal" for the cells to become damaged in the first place is more difficult to say, but I suppose that it depends on the kind of usage the battery gets. In my case, I ran the machine with the power supply attached most of the time, I never made it work very hard, and I even used a small cooling fan when I ran the machine outdoors in hot weather. I suspect that's why I got over 5 years of use out of the battery.
But nothing lasts forever, and that aging battery was seriously stressed by the Leopard installation. I'm now convinced that it was its undoing. If there's a lesson to take away from this, it's probably that heat kills batteries. Eventually, the battery will die a peaceful death by exhausting its own ability to hold a charge, but until then you can reduce the chance that it will die violently in the battle of the bulge by keeping it as cool as possible