Does anyone know how I can achieve this? briefly had a look through blockchain but not sure where to start...
Its not possible for wallets*, but for addresses. I made a little java tool [1] a while back (sadly for an idiot, but maybe it can help you) that takes a list of addresses, checks blockchain.info's API for the balance and writes it into a file. You could use that to get the balances for each of your addresses and make a sum of the result to know how much BTC is in your wallet. But honestly, why does your wallet client not show the amount of BTC you have?
*wallets do not exist on a protocol level, but are an abstraction to help humans handle multiple addresses and keys.
[1]
https://bitcointalk.org/index.php?topic=736607.msg8355029#msg8355029