Why is my computer shutting down for no reason?

My aluminum MacBook is about 2 years old now. I use it very often, so perhaps this is just normal? It turns off randomly, without warning, with more than enough battery power left. It's happened 4 times in the past month or so and I'm beginning to get worried! It just happened today, after I unplugged my adapter for about 15 minutes. I left the computer off for 4 hours. When I returned to it, I plugged in the adapter and turned on the computer...turns out there was still 55% of the battery left! I really hope someone can help me figure out what the problem is...

Here is what my System Profiler says about my Power:

Battery Information:

Model Information:

Serial Number: DP-bq20z951-3a2c-4a24

Manufacturer: DP

Device name: bq20z951

Pack Lot Code: 0000

PCB Lot Code: 0000

Firmware Version: 002a

Hardware Revision: 0005

Cell Revision: 0100

Charge Information:

Charge remaining (mAh): 2338

Fully charged: No

Charging: Yes

Full charge capacity (mAh): 3245

Health Information:

Cycle count: 551

Condition: Good

Battery Installed: Yes

Amperage (mA): 385

Voltage (mV): 12293

System Power Settings:

AC Power:

System Sleep Timer (Minutes): 15

Disk Sleep Timer (Minutes): 10

Display Sleep Timer (Minutes): 15

Automatic Restart On Power Loss: No

Wake On AC Change: No

Wake On Clamshell Open: Yes

Wake On LAN: Yes

Display Sleep Uses Dim: Yes

Battery Power:

System Sleep Timer (Minutes): 0

Disk Sleep Timer (Minutes): 10

Display Sleep Timer (Minutes): 0

Wake On AC Change: No

Wake On Clamshell Open: Yes

Display Sleep Uses Dim: Yes

Reduce Brightness: Yes

Hardware Configuration:

UPS Installed: No

AC Charger Information:

Connected: Yes

Charging: Yes

Thanks for reading!