I'm having a problem with the battery when I shoot video on my 50D: I can use Magic Lantern without any problem during hours with the same battery, only if I start shooting the battery runs out in approximately 2 minutes.
I tried with various fully charged and working batteries, all in perfect condition. The same thing happens. Again, if I don't shoot video, I can use the camera with magic lantern during hours. Unsinstalling and reinstalling magic lantern did not change anything so far.
Someone already had the same issue, but the topic was labelled "invalid". So if anyone had any idea of what I could do to fix this, I would be very thankful :)