As someone might know, the N950's battery can be upgraded to BV-4D 1400mAh. Let me just quickly introduce it.

From the specification sheet, the N950 uses BV-4D 1320 mAh battery. This is also the same as the early prototype of N9-00. (Click to see the picture.)

However, as the orginal N9-00 Deli was canceled as a consumer device, it became N950 as what we see now. Nokia downgraded the battery when ship the device to BP-4L battery, at 1200 mAh.
This can be confirmed in this page.

There exist some early BV-4D 1320mAh battery on ebay, listing as battery for N9-00. (Although don't know if it is true or not.) This raise some confusion between N9-00 (N950) and N9-01 (N9). N9 uses BV-5JW 1450mAh but N950, indeed, uses BV-4D orginally.
Even Steve Litchfield in AAS was confused about this - see the comment of this link!

Finally, the improved BV-4D 1400mAh is used in 808 Pureview. And I did find a trusted source for the genuine BV-4D battery, without buying a 808.

I'm excited and currently waiting for the delivery. Ideally, the battery in current N950 will be improved from 1200mAh to 1400mAh, which is a big improvement.

I will give the result once I tested the new battery.