Generally, you’d want to keep your solar battery stored in an area that doesn’t get too hot or too cold. Low freezing temperatures can affect your solar storage efficiency as it will limit the amount of energy you are able to discharge the colder it gets. In warmer areas such as places in California, it will be fine to install the solar battery in the garage. Find a professional solar battery installer that can help you decide on where the best location is for battery storage.  Another reason to keep in the garage is that it would be closer to your wiring unit and electric panels within an enclosed space. Leaving the battery system outside exposes the wiring to the environment which can get worn down faster.