D300 Inconsistencies with Interval Timer

[iflynething]

Sometimes, usually more than now, I try to use my interval shooting method on the D300. When it works it works great, but I can never tell when it will.

I have the camera to use the grip battery first and then the one inside the body. I have tried switching that order to see if I am able to use the interval function. Sometimes it available to use and sometimes it's not. I"m not sure when that time is though!

I thought it might be if the battery is above a certain level, I would think 50% but that's still not the case. I have had almost a dead grip battery and it will work. At other times, I'm pulling power from the body battery and it won't be available to use.

Any help?

~Michael~