For more detail on battery enclosure and powershed design click here.
If you are off-grid batteries are essential unless you have a large 5kW+ hydro resource. If you have adequate intermittent all year generation from opposite renewable energy sources (such as solar PV and hydro) then you can often manage with a smaller battery bank (provided you are frugal during times that are overcast and dry and/or are prepared to use a fuel generator).
Remember most battery sales representatives do not live off-grid through a NZ winter (where the sun may not shine for days). Their advice is often based on a sales blurb and margins and not always on a solid customer experience.
There are many battery types on the market, if you intend to live off-grid and want the perfect battery experience and no limits on your power consumption (and no 2nd mortgage to go with it), then we suggest you do not live off-grid. If you want the freedom to use plenty of power whenever you like you will need the grid to support your system automatically. If you are prepared to be careful at times, invest in a renewable energy generation system large enough to power your home all year then existing battery technology can work well as at cost of about $1-2000 NZ per year.
If the grid exists already at your home we do not advise you go off-grid. You can consider grid-tied or grid-assisted systems which may require no battery or only require a very small battery.