In Star Trek Beyond there's a pretty cool scene where Captain Kirk and Chekov head toward the wrecked Enterprise with their prisoner, Kalana. When they see it from a distance Checkov immediately pipes up and says, "She still has power."
How did he know the saucer section still had power? I might add, it's daytime when they see it first.
As a bonus question, how in the world could it still have power?
The quote from the scene pictured above is actually
Chekov: She may not even have power to the Bridge, Keptin.
Kirk: She still has a few tricks up her sleeve. [beat] I'd bet on it.
It's not until nighttime (and at the point when they're close enough to the ship to be able to see and hear individual features) that Chekov then exclaims...
Chekov: It looks like it has power
As they enter the ship, we see that the bridge's emergency lighting is still working (albeit sporadically). That, presumably is what Chekov could see from the ground.
