There are important considerations to keep in mind when selecting a deep-cycle battery. Choosing the right battery will result in the greatest performance and overall return on investment.

Maintenance
If a site is easily accessible, then deep-cycle flooded batteries are a good choice due to their low cost and widespread availability. If the installation is in a remote area where regular maintenance cannot be guaranteed, then maintenance-free, deep-cycle AGM or gel batteries are the best options despite their higher cost.

Chemistry
In areas where batteries often operate at partial state of charge, the addition of carbon additives has been successful in extending the life of deep cycle batteries. When batteries operate in off-grid systems or in locations that experience an unstable grid, they are often not fully charged on a regular basis. This quickly diminishes the overall life of the battery, but carbon additives can help prolong battery life and avoid costly frequent battery replacement.

IEC testing
Look for IEC and third-party test results. Select a manufacturer that employs outside testing companies to ensure the accuracy and validity of cycle life data. Testing to the IEC 61427 standard ensures the batteries meet the rigors of the deep discharge and recharge cycles of renewable energy applications.

Cycle life
This is measured as the number of discharge/charge cycles the battery can provide at a specified percentage of its rated capacity. Batteries from different manufacturers may have the same capacity rating, but design, materials, process, experience and quality control heavily influence cycle life performance.

Capacity
Review the capacity of a battery to ensure it is properly rated for the application. A battery with insufficient capacity will over-discharge on a regular basis and have a shorter life. An oversized battery also is a poor choice because it will cost more for no added value.

Brand
With many deep-cycle batteries on the market, choose a battery from a company with a reputable brand and a history of engineering and manufacturing quality deep-cycle batteries for renewable energy applications.

Price
A battery with a low price is attractive, but if obtained at the expense of quality and cycle life performance, the cost over time will be significantly higher due to frequent battery replacements. It’s important to consider issues other than price when deciding on a battery for renewable energy applications.