Although all battery manufacturers use the same general processes, all batteries are not created equal. There are significant differences in the battery components used during the manufacturing process as well as the quality control processes each battery manufacturer implements within their facilities. Evaluating these differences is key in determining a battery’s longevity and performance, and this information can usually be found on a deep-cycle battery manufacturer’s website. If not, ask your sales rep or the battery manufacturer directly about specific manufacturing processes.
The working components of lead-acid batteries are their plates, which are made of lead. To harden the lead for use in a battery, it is combined with other metals (calcium, in VRLA batteries; antimony, in flooded batteries).
Lead oxide is used to produce the pastes, which include the positive active material (PAM) or negative active material (NAM) that is applied to a grid of lead that becomes the battery’s positive and negative plates. The chemical compositions of PAM and NAM are proprietary. Deep-cycle batteries have PAM and NAM recipes tailored for applications such as RE, propulsion (in EVs), or equipment like electric forklifts. Therefore, it’s important that a user understand what they want to achieve from their batteries—long float life or long cycle life. A battery’s design and paste formulations are customized for one or the other.
The battery’s lead grids are designed to hold the active materials (PAM and NAM). The grids also provide an electrically conductive path that enables the electrons to move in and out of the battery. Positive and negative grids are cast from molten lead alloys, and the patterns used in the design of grids vary from manufacturer to manufacturer. Grid designs and configurations help the current flow through the grid network, enhancing overall battery performance.
Once the positive and negative grids are pasted with PAM or NAM, they undergo curing, in which the paste is dried slowly. During this process, a bond is created between the paste and metallic grid, to develop an electrochemically active mass. Curing must be accomplished under precisely controlled temperature and humidity to produce a high-quality battery. The curing time can take as long as 72 hours to fortify the interlocking crystal structure of the PAM and NAM.
After curing, the plates are arranged in groups, alternating positive and negative. A separator is placed between each plate that prevents them from touching and shorting. The separator material’s quality and design are important factors in determining the battery’s service life. High-quality batteries use glass mat or rubber separators that reduce the chance of stratification, which is a typical mode of battery failure in renewable energy systems. Stratification is the process in which the acid concentration at the bottom of the battery becomes greater than the concentration at the top. If not addressed, stratification will destroy a battery.
After the appropriate number of positive and negative plates are stacked, they are placed into a plastic case, which contains one cavity for a 2 V cell, three for a 6 V battery, or six for a 12 V battery. The number of plates depends on the specific capacity of the battery being built, i.e., the greater the amp-hour capacity, the larger the number of plates. The positive plates are then welded together at the top, as are the negative plates, forming a single cell assembly. In multiple-cell batteries, each cell assembly is welded in series or in parallel to determine the battery’s voltage.
A cover is then heat-sealed to the case. The quality of this seal is important—if poorly done, the seal’s integrity can be compromised, leading to future problems such as breakage and/or separation of the lid from the battery case.
Once battery assembly is complete, the battery goes through “formation.” The formation process involves filling the battery with a solution of sulfuric acid and distilled water. The battery is then given an initial charge, which preps the battery plates for operation. Formation usually takes several days to complete; the greater the battery capacity, the longer the formation period.