Protein "fridge" life

[cloak33]

Any body know how long a pre-made protein shake will last in a fridge or cooler? Reason I'm asking is because a) I have no idea if whey protein starts losing it's potency once it's been mixed with water, and b) I'm always on the go and it would be easy to pre-mix a couple of shakes in the morning and bring them along with me.

Any thoughts?

Thanks