New cylinder - 1.5k NZD + half day of labour (so another $500). My current one stores about 6-8 kWh.

15kWh battery - 5.5k NZD + and hour of DIY.

So technically battery is more expensive but more useful.

Also easiest with water heater would be cranking up the temperature, but I really hate dealing with scolding water coming from taps (especially with small kids around).

Another thing with battery I can charge with whatever solar excess I have, but with hot water my only option is 16A.

Either way I do not care ATM - I export using spot price which has been 2x of what I actually pay for power - https://www.emi.ea.govt.nz/Wholesale/Reports/W_P_C?DateFrom=...