Without power or an internet connection you can't validate that the btc hash is unspent, avoid double spends, or validate that your taking ownership of it made it to the blockchain and was confirmed for a few blocks.
Sure you can transfer the private key from one device to another, but (a) you can't know the other person didn't retain a copy of it and (b) you would be limited to spending the exact amount you have in an existing transaction because you couldn't send a transaction to the chain that splits it.
