Voltage sag in relation to watts

Hi!

I got a question about the voltage sag in relation to watts/amps. I don't know what's wrong with my LiPo's but I've seen a voltage drop to 30V. (10S LiPo, 37V nominal) Anyway... I'm pulling 4000W, 133A and the voltage drops to 30V. But, what if the voltage of my LiPo would only drop to 37V?
Is there any way to calculate how many watts I would pull? It isn't 133 * 37 = 4921Watt, or is it? Because the amps will fall, I think?


Patrick