Most TCs are electric, and with attitude and heading gyros relying on an
electrical source all attitude info would be lost if the electrical system quit,
Oh that. I have a dual battery system and my EFIS-D10 has its own
internal backup battery to last an hour. The dual batteries have
40amp-hour total capacity and normal flight current is only about 12A.
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http://www.abri.com/sq2000