Computer help forum: PLEASE HELP!! laptop battery--what kind?/price differences?

Hello,

I need a new battery for my laptop--an HP Pavilion dv6-1355dx (the battery is completely dead--can't even charge it now). I found one I liked at BestBuy.com, item name "Laptop Battery Pros - Lithium-Ion Battery for HP Pavilion DV4, DV5, DV6, and CQ60 Laptops". It is $120, on sale for $87. However, I googled the phrase "laptop battery HP Pavilion dv6-1355dx", and all the websites and Google Shopping Results that came up showed prices ranging from $17-$65 (most in the $30-$50 range).

So now I'm completely confused...
1. Why the huge difference in PRICE??
2. What is DIFFERENT about the one I found at Best Buy that makes it so much more EXPENSIVE?? (and that model is just MID-range for the laptop batteries at Best Buy...)
3. Is it just that the Best Buy one is a lot BETTER?? (battery lasts longer between charges and/or has a longer life in general??)
4. But then, it's weird that no pricier batteries (over ~$65) came up when I did my google search--why is that??
5. I didn't realize that there were other companies (i.e., non-computer brands/manufacturers) that make laptop batteries... Is it better to get a battery made by a COMPUTER manufacturer/brand (HP, in my case) vs. a NON-COMPUTER manufacturer (like Laptop Battery Pros)?? Or does that not make much difference??
6. Aside from battery LIFE, are there any OTHER FACTORS to take into acount when choosing a battery for a laptop??
7. Are ALL (or MOST?) of the laptop batteries made today the LITHIUM-ION kind?? (that's the BEST kind, right??)

If you can, please keep any language you use as simple/"not-too-technical" as possible--in case you can't tell, I'm not all that tech-savvy...

I've been without a computer for over a week now, so I really need to get a battery as SOON as posible--PLEASE HELP!!
(And please forgive my asking so many questions--as well as my ignorance!)

Thanks!!
~Shanna