I have a Droid Bionic and I keep it in an Otterbox Defender case. I would like to get the extended battery but am concerned that my Bionic might no longer fit within my Otterbox. Has anyone tried this?
No.
My friend got an extended battery so I tried my case with his phone -- the extended battery is really large, so it won't work. Which is a shame, because the Otterbox Defender case is so large that a hypothetical extended battery Otterbox Defender wouldn't be significantly bulkier than the current Otterbox Defender (regular battery).
If Otterbox made a Defender case specifically for the Bionic with the extended battery, I would buy both that case and an extended battery. I guess that the market for that specific case is just too small.