How much will adding an extra hard drive to my MacBook Pro affect battery performance? I have a current MacBook Pro 15" i7 2.2Ghz with a 500GB 7200RPM (default) hard drive.

I am thinking of replacing both the current hard drive and the superdrive with two Seagate Momentus Hybrid 500 GB drives and placing them in RAID0 for optimal performance.

Now, I don't think performance will be a problem, but how about battery life? Are there any examples of users who already have done similar things and noticed the effect on battery life?
Having a second hard drive will certainly decrease battery life by a noticeable amount. Behind the CPU and LCD, the hard drive is the largest drain on battery.

A word of caution: RAID 0 is almost never a good idea, unless you'll be doing backups constantly and don't mind being totally down if a drive fails. You'll get better performance from an SSD and you'll be able to keep your optical drive.