I am using an Arduino Nano in a project running off a 3s Lipo (max 12.6 V fully charged), and and am wondering if it is safe to power the Nano directly from this using the VIN pin and internal regulator. The Nano's store page contradicts itself, listing the safe input voltage on VIN as 7-12V under the "Tech Specs" header, but 6-20V under the "FAQs" section. Does anybody know which is correct? I should not be pulling much current, it will only be powering the Nano, an IMU(MPU 6050), a Bluetooth module (HC-06), and 1 LED.
12.6volt on V-in should still be ok for a classic Nano, but you're in the danger zone.
At that voltage you can't power anything from any pin without the chance of overheating the onboard 5volt regulator. Although the IMU and one LED could just be ok.
Powering the BT module from the 5volt pin almost certainly will get you into trouble.
It's wise to get a buck converter to drop that 12.6volt to 5volt, and power the Nano on the 5volt pin. The BT module can also be powered from that 5volt buck converter.
Leo..
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I agree that the best course is to use a buck converter to drop the voltage to 5V to feed the 5V pin. The built in Nano voltage regulator will provide little current before it overheats and shuts down if asked to drop over 7V.
Life was easier before they modified that page as the 6-20V was described as the absolute minimum/maximun values.
If in doubt, use the more limiting values.
I agree as well on the 5V buck converter.
I continue to advise that it is not wise to use the "Vin" - or the "barrel jack" on a UNO/ Mega 2560/ Leonardo - for any project.
Even if you get away with it to start with, there may be a temptation to "just add something extra" and mysteriously come to grief. 
Some recent Arduino designs do have a more useful switchmode regulator however.
Ok, I'll get a buck converter then. Thanks!
Bear in mind too , that any clone may not meet the official specification
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