After battery replacement, apple watch will not boot past Apple logo

This is my first apple watch repair… I replaced the battery and everything seemed to go perfectly, but upon charging the watch back up —- the apple logo blinks in 12- 15 second intervals and no amount of holding the dial / power button seems to make it boot correctly. Any ideas for this fledgling repair man?

Much appreciated.

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Does it do this with the old battery? Where did you buy the new one from?

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Thanks for the reply.

The old battery held zero charge, and has since been thrown it out (I didn’t know to keep it ).. I bought the replacement battery from here, Ifixit. I think it’s successfully holding a charge?

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