Hi Theresa, thanks for getting in touch. The Piano Tube Humidifier comprises of a sponge-like material that absorbs water but doesn't allow it to leak it back into the piano (instead, evaporation gradually removes the moisture, helping to humidify the air within the piano).
It's designed to be fitted horizontally above or below the action inside the piano. It doesn't require batteries, but would periodically need to be removed from the piano to be refilled with water.
We strongly recommend the piano humidifier is fitted by a professional piano tuner or technician. Our normal price includes installation (within the UK mainland) but, if you don't require this, you can choose to order the humidifier only, for self-installation.