My wife's MacBook Pro has begun shutting down unexpectedly, at seemingly random intervals. This started occurring after I (very carefully) upgraded the machine from 4 GB to 8 GB of RAM and replaced the old battery, which had reached the end of its life.
The shutdowns are instantaneous, while there is plenty of power left. It's as if the power button was held down. It has happened twice when a USB hard drive was connected, but that might have been a fluke. I haven't been able to consistently reproduce the issue.
Does anyone know how to debug this issue, like if there are any logs of unexpected shutdowns that might provide some clues as to what's going on? Any pointers greatly appreciated.
I'm not sure if this is relevant, but the same machine was having a different issue with sleeping until I upped the RAM and changed the battery. This issue has since stopped happening.
Edit: The problem we're experiencing sounds very similar to this blog post.