Hmm, thanks for the warning. I suspected it, battery might scratch the surface of dx50 on every push and turn. So I guess spare battery is not safe for portable use, better to keep it charge and replace when occasionally, because if we frequently change it, I'm not sure how good is back flip of dx50 after some time it might not stay in place and loosen up pretty much. Also keeping the spare battery without any charge for very long time will make the battery to leak acid and it will also explode and disfigured. The free battery is more trouble than worth I guess, 2nd and 3rd batch can consider themselves lucky!
why do you need to use otterbox for dx50?..just pop it in the sling bag and there's you go...spare battery is just something ibasso can offer us to compensate for the late delivery.... but something useful where when they fix the battery indication feature :P