It depenss on the formula. Some say dont if your baby has already had some. Some say do. Check on the instructions on the formula container and the doctor
I have been told to only warm it once. So im going to say no
Yes. But if I would only reheat once. If my son didn't drink it all the second time, which hardly ever happened, I just tipped it down the drain.
Even if it already been warmed up
Yes. On the one I use it says to use within an hour or store in refrigerator and use within 24hrs.