Petzl Duo battery drain question

[Kevenater]

I have a Petzl Duo with the 8 led drop in upgrade that came out several years ago. I haven't caved with the light in about 5 years or so but use it around the house sometimes. I've noticed that when I leave the batts in the batt compartment on back of my helmet they drain pretty fast. I started taking the batteries out and they don't drain. Btw my setup is the petzl explorer that comes with the carbide and the duo with the plastic batt compartment mounted on back of the helmet. Seems like for some reason the light is draining the batts somehow when left in the light. Any ideas why this would happen? Thanks