I was able to get a Nokia Lumia 800 as a developer gift from Nokia. and it seems that it doesn't have the common battery issues that people have.
At first it did, would shut off at 20%. Messed around with just connecting and getting data using DPM and Nokia Care Suite after updating it to Mango 8107 and it started working just fine.
I am on the 11451 firmware and my Diagnostic app steadily always shows 1516-1520mAh for full charge. Only thing weird, it says "Charged 65535%" for the battery percentage. I have checked it daily for the last week, no change to the full charge capacity.
Here are my specs to help, and a shot of my phone's diagnostic screen.
Carrier: AT&T USA
Firmware: 1600.2479.7740.11451
Hardware Revision: 112.1402.2.3
OS: 7.10.8107.79
Nokia Care Suite Info
Product Code: 059J3G0
At some point I was able to pull the Variant and it was something like "RM-801 EURO MATT BLACK" or something, I can't find it atm. I think it was in DPM, but I updated my DPM and it won't launch now.
Also, there isn't an 11500/11501 release on DPM for this model, or on Zune.
I thought this could be useful for those trying to figure stuff out.
Images of my Diagnostic app: