I have the same problem. Updated to Yosemite about two weeks ago. File Vault encryption started and got about 90% done. Machine is running hot and getting nowhere. runs out battery at about 1% per minute without charger attached. File Vault estimate to complete varies up to 140 DAYS. I already spoke with one of the Geniuses at the Apple Store. She said give it some time to finish encrypting. That was a week ago. HELP
I am running a 13 inch Macbook Air mid 2012.
I want to stop the encryption (or finish it) then turn off the encryption again.