Does the Casio FX-451 have a battery? Or is it strictly solar?

From: Michael Craft
Email: mcraft@udri.udayton.edu

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I have a Casio FX-451M. I’ve owned it since 1985. A *GREAT* calculator. Anyway, I have always thought it was strictly solar powered. But I’ve read in a couple places that there’s also a battery. Is this true?? Should I replace it? How? Do I simply pop the metal plate off? Also, does anyone have a copy of the manual for this calculator? Thanks