Probably already been said but just looking at the form factor and what it's being asked to achieve, portable battery life is going to be horrible.
Consider all of the things drawing power from the device:
- Phablet size HD display.
- Tegra APU.
- Multiplayer functionality of some sort - WiFi, most likely.
- Read/write to system memory and cartridge systems (people underestimate the fact that this does actually contribute to power consumption).
- Wireless connectivity to the detachable controllers.
In a package that's narrower than the current N3DS? And people are jumping on the hype train expecting this thing to function, portably, as equivalent to a PS4 (seriously, the comments on Nintendo's FB page are doing just that). Unless Nintendo has a time machine from which they've been able to acquire futuristic battery tech, the likelihood of this thing lasting more than 3 hours in pure portable mode is slim.
As a connect-to-TV device, I'm interested but I'm HIGHLY skeptical of both the portability and performance. I'll mark myself as cautiously optimistic but not enough to preorder the system until I see some actual performance reviews and see exactly what games are coming to fruition (as, unlike most of Nintendo's FB feed, I'm not enthused about a port of 5 year old Skyrim).