Honestly, I'd just make my own pack. That is an absolutely insane price for a battery pack. I paid $40 for an 8 cell pack for my Magicshine, it's over 2 years old now and still going strong.
Just buy a generic pack and solder on the connector from the old dead pack. 10 minutes work, tons of money saved.
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Work: the 8 hours that separates bike rides.