Aotearoa / New Zealand

Same. I've been wanting to get some sort of rain water collection system going. The new place we're moving into has sort of a raised garden bed in between two retaining walls - maybe something could be buried there in the future.

I don't have any experience doing anything like that, but I don't see why it wouldn't be possible. Depending on what type of battery it takes, there will be a voltage that the whole thing is designed to work with. It's would then be a matter of setting up a small solar panel -> Charge Controller -> Battery System, and then making sure the output voltage from your battery is near enough what the unit requires. This can be done using voltage regulators to bring the voltage you are supplying, up or down to the required level.