Check out the application Carbon Copy Cloner. Fast is a relative term (but it is easy); speed depends on the interface and drive. If you want to transfer, you're gonna need an external drive. Best idea is to buy an enclosure, put the new drive in, copy over to that drive, then pop it out and stick it in the computer. Unless you already have an external drive handy, I suppose.
Alternatively, you could use Migration assistant- pop the new drive in the computer, toss the old one in the enclosure, boot from either the enclosure or a CD and reinstall the OS, and then migrate your files over. This is usually a better option for SSDs from what I've heard- I don't know if it matters either way for a regular HD.
As for battery life, a bigger hard drive won't hurt battery life- theoretically, it might improve it slightly because the data will be closer to the edge of the drive. A faster hard drive might- results may vary- and an SSD will most likely improve battery life, depending on your tasks.
One more thing, OP: this might be greedy me talking, but you should look into upgrading to the newer model. It's worth a shot for a free extra 50 GB, better battery, faster processor, and slightly faster graphics chip. If you can, call or pop into an Apple store and see what they can do for you- we've heard good things about upgrading when a newer model is released.