Kristin,
The surge rating means it will tolerate that voltage for a *brief* period, not long-term. You'll need to find something with a higher voltage rating. While you're at it, better pick up a new battery for the ol' calculator. 25 * 1.414 = 35.35V , not 28.535V :-)
Your plan for sorting the phase on the secondaries is spot on.
Regards,
Ray L.