Sorry, not sure if this has been posted yet, didn't readily see it.
My question is this: I recently purchased the Infuse and a Ballistic case to protect it. If I get the upgraded 3500mAh battery will it still fit in the case?

Not without modifications to the case.

By the way, I have the same case and I found another minor mod that needed to be done. The prox sensor will think you ALWAYS have the phone up to your face when you use this case. You need to pop the front cover off, use a razor/xacto knife and carefully cut awat the film from the camera/prox sensor area to solve this. Then, to reseal the case properly, use a small piece of adhesive backed foam and cut away the same shape with it on the inside of the case, with the adhesive facing the case, not the screen. This causes the foam to compress against the screen once its back together keeping dust out, and at the same time allowing the prox sensor to really see your face.

I just got my extended battery, so once I complete the case mod I will post it here for you.

Thanks. Looking forward to the results of your modifications. Although I don't think that we have the same Ballistic case. I do not seem to be experiencing the situation that you mentioned. I am using the 3 three layer black and red case (the one that does not come with a front shield). The only thing I have on the front is the clear lcd shields designed for the infuse. The front camera and speaker area are cutaways.

Moderator.... This issue can be closed. I no longer have the phone or the issue. Thank you...