Everything works with electricity!
If power fails everything fails:
- you can't use bitcoin or dogecoin because you can't broadcast a transactions
- you can't use a CBDC because of the same thing
- you can't use a card because all the banks are offline
- and surprise, you can't use cash because every chain store runs on electricity and they will not be able to issue receipts not will a cashier do the math for your groceries and then wait two days till the power is restored to do the balance for all those payments.

Other than mom&pop shops with low volume that will take cash nothing else will run, every big business would rather lose than order their staff to take money and write it down in notebooks only to insert another day in the system, it's way too much trouble for one day of income.

As far as I know, the ECB is not claiming that the digital Euro will be able to operate without electricity, instead they are saying that they can operate offline without a constant internet connection. Because to be able to use it, we also need electronic devices, applications...so it is absurd to say that it can work without electricity. Also, using Digital Euro without internet is just theoretical and we will have to wait until it officially goes live to know for sure.

Both CBDC and bitcoin are digital currencies, digital assets, so they cannot function without electricity. I heard that bitcoin can work without the internet, but I don't think it can.