Hi Shaunchy,
Any error messages recorded in Event viewer\Windows logs\system?
If Bitlocker lost power source during encryption or decryption, it will resume encryption or decryption after power source is available. So I suspect the issue is not related with your power issue, it would be more related with hardware failure.
We could try to repair Bitlocker through repair-bde command line as administrator. For details, we recommend to refer Scenario
16: Using the BitLocker Repair Tool to Recover a Drive
If it is not able to repair Bitlocker with this command tool, it would possible with hardware failure and would not possible to get your data through it.
Bests,
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