15 R2, where to get the genuine battery?

Hey there,

I am a Dell Alienware 15 R2 user. From the past few days, i am unable to run my Alienware on battery. I have to connect the charger to start it and i see the following error every time:

"The battery is temporary disable, please turn off the computer and try again when the unit is back to operational temperature. Strike the F1 key to continue, F2 to run set up utility"

I contacted the support and they clarified that although my pro warranty is still there, they can't replace the battery as it is not covered in the warranty. They told me that the battery has to be replaced in this case. I asked the sales team to send me the quotation but i didn't get it yet. So, i decided to do some research on my own and buy it from somewhere else. These are my concerns:

1. How do i ensure that the battery i am trying to buy online is fully compatible with my system?
2. How do i ensure that the battery is genuine?
3. Where can i see the part number?

Kindly assist me.

@Anonymous