Aimpoint Replica loosing intesity

[Wolfe117]

I have a Aimpoint replica from Guarder. It has fairly new batteries and doesn't have any exterior damage. When I turn it on at a game it has good intensity on the red dot. However, after maybe 10 to 20 mins it loses intensity to the point where I simply can't use it anymore. If I turn it off and then back on it comes up with the same low intensity. However, if I leave it off for a while and then turn it on it comes up with normal intensity (for a short while again). Can anyone help with figuring out what's wrong with it?

[MMMiles!]

Sounds like the batteries are on their last leg. Try a new set for comparison.

[smjbmw]

def battery