We see a few times where Tony Stark with without a power source for his chest:
- When he has Ms. Potts connect the Mark II chest piece
- When Stane removes his Mark II chest piece
- When the Mark I chest piece runs out of power
- When he puts in another cartridge for his Mark III chest piece
The first time with Ms. Potts he goes into cardiac arrest immediately after she removes the copper coil.
The second time when Stane removes it, he is temporarily paralyzed (for 10-15 minutes), then crawls down the stairs, struggles to get the Mark I, and eventually gets it into his body. That was maybe 30-45 minutes?
The third time the Mark I appears to be completely out of power (or very near to the point). He doesn't have a backup device ready, because if he did he would have used that back at his house instead of the Mark I. By the next morning he has a new device again, but there was some amount of time for him to get retrieved from the roof, get back to his house, and built another chest piece.
Just how long can he survive without the chest piece?