Well, according to your scenario, both engines have flamed out.
30 minutes of battery power (if accurate) will be more than enough for the remainder of the flight...err...glide
- and the least of your worries.
Air Transat 236 - 19 minutes between final engine flameout @ 34,500 feet and landing.
Air Canada 143 ("Gimli glider") ~18 minutes between flameout @ 31,500 feet and landing.