[Kenwood] Weird behavior from a TS-850SAT

[Joe Moraine]

I had a strange occurrence on my TS-850.  I discovered all SSB signals 
were equally understandable on BOTH USB and LSB.  All signals were 
intelligible on BOTH sidebands.  I did a complete "reset" of the 
computer and all is now fine and normal.  What would cause this to 
happen?  Also, has anyone replaced a battery in the TS-850?  Is it easy 
or difficult?  Thanks for any suggestion on these 2 questions.