Low Battery Life (Early 2009 MBP)

Hi -

I have a 17" MacBook Pro 5,1 (Early 2009). Last year, I added a WD6400BPVT hard drive to replace my stock 320 GB drive. This summer, I noticed that my battery life had gone from 5-7 hours on a full charge to less than 4. Now, for about 9 months, I did have my system almost always connected to the MagSafe adapter, but it started becoming more mobile again in August. System Profiler shows the following information regarding the battery:

Model Information:

Serial Number: 9G91707614M0A

Manufacturer: DP

Device name: bq20z951

Pack Lot Code: 0000

PCB Lot Code: 0000

Firmware Version: 0042

Hardware Revision: 0001

Cell Revision: 0119

Charge Information:

Charge remaining (mAh): 10871

Fully charged: No

Charging: No

Full charge capacity (mAh): 11700

Health Information:

Cycle count: 367

Condition: Normal

Battery Installed: Yes

Amperage (mA): -1713

Voltage (mV): 8104

I did all the normal battery troubleshooting: reset my Energy Saver Preferences, reset the SMC and PRAM, let the battery fully drain once, then fully recharge, all without effect.

It finally irritated me enough that I made an appointment at the Genius Bar to have it looked at, and so I reinstalled the stock hard drive... and my battery life is back to normal on the indicator.

Other than the hard drive, the software differences were that the 3rd party drive was fully updated with 10.7.2, and all iCloud services, and I ran all Software Updates the day they came out, including iLife '11 and Lion on launch days.

I am currently in the process of updating and upgrading the software on the stock drive, then I will let it run, but do any of you have any thoughts about what could be causing it?

I find it hard to believe that the hard drive would use enough power to lower the battery life by up to 3 hours, but that's what it's looking like at this point.