Macbook Pro keeps shutting down randomly

Hello-

My 15" Macbook Pro (Late 2011) has started unexpectedly and randomly shutting down. I recently installed Mountain Lion and it started after that, and only seems to happen when running on battery power. I've tried an SMC reset multiple times and that doesn't seem to help. I'm running a 2.2 GHz Intel Core i7 with 8 GB of RAM, updated to 10.8.2.

Based on my battery report, I don't think that's the issue:

Model Information:

Serial Number: D861153011CDGDMAC

Manufacturer: SMP

Device Name: bq20z451

Pack Lot Code: 0

PCB Lot Code: 0

Firmware Version: 406

Hardware Revision: 2

Cell Revision: 157

Charge Information:

Charge Remaining (mAh): 5314

Fully Charged: No

Charging: Yes

Full Charge Capacity (mAh): 5924

Health Information:

Cycle Count: 161

Condition: Normal

Battery Installed: Yes

Amperage (mA): 1316

Voltage (mV): 12439

Anyone have any suggestions other than an SMC reset?