In blockchain, there's an option to import an address under the Address menu. I tried to import my wallet from my old android app to the new wallet in Blockchain, However it appears as "Watch Only" and it doesn't really transfer the funds to the default Blockchain wallet I created.
I get a message showing "0 address was successfully transferred to My Bitcoin Wallet. Would you like to archive this address now?"

I then saw that the transaction fee takes away about $6AUD (bare in mind I'm only experimenting with $7.23AUD which is 0.00226BTC)
So, if I want to transfer my whole 0.0026BTC from one wallet to another, it tell me to use total available minus fee: 0.0017176 BTC, which is 0.0005424...

Does it make sense?
It also asks me for the private key of that wallet I have on my android device. I have not idea what is this private key.