Envirolet® 12VDC Battery models draw less than 0.60 amps total. Each Fan (there are 2) draws approximately 0.26 amps.
The Fans should be operated all of the time when the System will be in use. For optimum performance, the Fans should also be running when the Envirolet® will not be in use for any period up to 2 weeks, e.g., a weekend cottage.
A normal marine, deep-cycle, 12v battery will last approximately 18-21 days on a full charge with both fans running. A Solar Kit is a good way to keep your battery charged.