[Seraphim]

I have a BL-5C working in my glacier now.

You are correct, that the back will not fit completely on, however if you use a good knife to cut one of the retaining tabs on the front of one side, the battery will slide on snuggly with a slight bulge at the top mid portion of the battery cover.

It's not very noticable unless you turn the player sideways and look for it.

I wanted to give it a try because of the large difference in milliamp hours that the 5C offers over the 4C.

I've had it playing WMA files for the last 2 hours, and will see how long it plays.