When the formation process is complete, the battery is tested to confirm it meets the manufacturer’s specifications. This is called “end of line” testing, which ensures all electrical connections are working properly and there are no obvious defects. The battery is then cleaned of any residual acid on its external surfaces, labeled to be in compliance with all necessary regulations, and prepared for shipping.
The differences in the manufacturing processes for a deep-cycle battery can have a profound effect on its performance and life, as seen in the images that show high- and lower-quality batteries.
Both had the same rated capacity, were the same age, and experienced identical service under controlled conditions. However, the battery on the left has aged far more gracefully than the one on the right. Why? The battery cell on the left has a moss shield on the top of the plates, which prevents the plates from expanding and shorting out at the top of the cell. The absence of a top shield on the other battery eventually caused short-circuiting, leading to lower capacity and a shorter life span. The battery on the left also featured a paste formulation specifically designed to optimize use of the battery’s active material, resulting in sustained battery performance over a longer period of time.
Besides the presence of a moss plate, the design and use of a battery’s grid and separators are equally important. Corrosion can quickly kill a battery, and the thicker a battery’s grid structure, the greater its resistance to corrosion. It also is important to ensure that the grids are cast, rather than stamped. Cast grids have no hairline fractures, which can cause the battery to fail prematurely.
In addition, separators between the battery plates should feature wide channels to increase the flow of acid, which enables optimum battery performance. Batteries that feature separators with wide-channel designs will also offer greater resistance to stratification.
An essential component of determining the quality of a deep-cycle battery is the manufacturer’s investment in independent third-party testing. This data provides valuable information on product performance, and validates a manufacturer’s product claims. Independent, third-party data obtained from testing batteries per industry-recognized standards, such as by the International Electrotechnical Commission (IEC), allows consumers to compare products from different manufacturers, and can be found on some battery manufacturers’ websites.
For an RE application, the two parameters of critical importance are amp-hour capacity (commonly at the 20-hour rate) and the number of cycles the battery can deliver to a given depth of discharge (DOD)—for example, 3,000 cycles at 50% DOD.
Once the short list of possible battery options has been created, the next task should be to ensure the battery manufacturer has not only a proven track record, but also builds quality into each battery it ships.
The type of battery you choose and the vendor you purchase from can have a significant impact on the performance, durability, and total cost of a renewable energy system. The battery bank in an RE system typically represents the largest equipment cost over the life of the system, so proper understanding of deep-cycle batteries is important to maximize the return on your investment.
Kalyan Jana is a senior applications engineer for Trojan Battery’s renewable energy group.