Strange D300 battery indicator problem

Lately my D300 started to show a low battery warning in the viewfinder. I'm using D300 with MB-D10, and this happens with fresh batteries, both in the grip and in the camera. The top LCD doesn't give any warning and shows that both are fully charged. During this warning the camera freezes for few seconds and then comes back to normal. Did anybody experience this, could it be a sign of some more serious problem?

Would appreciate any help.