I was freaked out that the D3s flashes "CHA" at the top of LCD display and low battery in viewfinder no matter which battery I put in. The end of my D3s? so sad I felt.
Well, actually, I just inserted a new not-formatted CF card. After formatting, everything goes back to normal. This is is the first time I ever "panicked" about this old trusty body.
Hopefully, anyone of you ever get into the same situation. Don't panic, all you have to do is FORMAt the card.