A lot depends on your soldering as well as the bars like ashleyb4 says.
I've got 3 sets of IBs (non exploding ones just yet - touch wood
). 2 go in - just and the third is a bit of a mallet job but still fits.
Due to fear of exploding IB's I've gone for Orion SHOs for 2008 spec - these fit no problems at all as they're fractionally shorter.
Older cells like GP3700s, VTEC 3700s or GP 3300s virtually slop about.
Buy hey - before long, we'll all be running LiPo anyway
