Deep Cycle Batteries are the key component in various types of renewable energy systems that require the storage of electricity. A battery is essentially a storage vessel for electricity. It is a critical component heavily relied upon by the system as a whole. A battery bank can provide a relatively constant source of power when the grid is down, or during periods when your photovoltaic system is not producing power. Although batteries are not one hundred percent efficient, they are predictable and stable enough for reliable long-term service.