I wouldn't expect the lounge to hang onto your bag - seems something of a security risk that the company wouldn't want to take responsibilty for.

Details of AKL domestic terminal left luggage provision is at the Auckland Airport website

Beware, the domestic location isn't open 24 hours which could be an issue depending on which 10 hours you'll be seeing Auckland. I've only used their location at the international terminal - the prices seemed reasonable compared to other international airports.