Why does my MacBook Pro suddenly die instead of remaining in sleep mode? I have a MacBook Pro 2.4 GHz Core 2 Duo (Pre-unibody) running Snow Leopard that fails to stay in sleep mode when the battery is run down to 0%.

This problem just started a month ago. The battery is new. It runs down fine and I get a warning when the reserve battery kicks in at 10%, but when it reaches 0, it goes into sleep mode for about 1 second and then dies.

When I boot back up, it tries to recover but fails and then just reboots as normal. I tried recalibrating the battery and I also tried resetting the PMU but to no avail.

If anyone has any ideas, I'm open to suggestions.
You may need to recalibrate for the new battery. Use the computer until you get the warning message. Then, shut down and plug it in. Let it charge fully before you turn it back on. Doing this will allow the system to calibrate for the new battery so that it can more accurately tell how much charge is remaining, which could help if it thinks the battery will last longer than it does.