Can I redeem one App Store gift card on more than one ipad?

They need to be signed into the iTunes Store with the same Apple ID. iTunes gift cards are redeemed on a per-Apple ID basis and not on a per-device one.

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You can redeem a gift card only once. If the iPads in question are using the same Apple Id, the Balance will be visible and available on both devices. You cannot redeem the same Gift card on more than one Apple ID.