Compare hour rate, temperature, cutoff voltage and discharge method before comparing capacity. AGM material data cannot replace complete-battery testing.
Hour rates and C-rate
Hour rates and C-rate
C10 refers to a 10-hour capacity rating, while C20 refers to a 20-hour capacity rating. These terms describe the capacity-rating method. They are not quality grades and do not mean that a battery can be discharged 10 or 20 times. A simple calculation illustrates the corresponding nominal currents: - For a 100Ah rating defined at C20: 100Ah ÷ 20h = 5A - For a 100Ah rating defined at C10: 100Ah ÷ 10h = 10A This arithmetic does not prove that the same battery will necessarily deliver 100Ah both at 5A for 20 hours and at 10A for 10 hours. Actual delivered capacity also depends on discharge current, battery design, and the test termination conditions. These examples cannot be used to derive a universal conversion ratio. Hour-rate notation should also be distinguished from C-rate notation. In capacity specifications, C10 and C20 commonly refer to 10-hour and 20-hour ratings. Expressions such as 1C and 0.5C describe current relative to rated capacity. The parameter field and its context determine which convention is being used.
Model-specific conditions
Model-specific conditions
Sacred Sun's SP Series page provides a useful manufacturer-specific example. It lists 5–33Ah products at C20 and 25°C, while 38–250Ah products are listed at C10 and 25°C. This shows that different capacity ranges within one series may use different hour-rate labels. These are specifications for the relevant Sacred Sun products. They should not be generalized to other brands or all lead-acid batteries. Temperature must be checked with the hour rate. Capacity tests are conducted at specified temperatures, and the Sacred Sun information cited above states 25°C. Performance measured or obtained under a different application temperature may differ from the nominal condition. Cutoff voltage is another essential boundary. It defines the voltage at which a discharge test stops. Different cutoff voltages represent different discharge depths and may produce different results. A comparison that records only 100Ah but omits the cutoff voltage is missing a key condition. The discharge load must also be clear. Constant-current and constant-power tests have different load characteristics. Ah data are comparable only within their stated discharge conditions. UPS selection additionally considers system voltage, power, discharge duration, and cutoff conditions. A constant-current capacity figure cannot replace verification under the intended equipment duty. Trojan's technical explanation of AGM battery ratings also states that amp-hour capacity changes with discharge current and uses different hour rates to illustrate that relationship. This supports the limited conclusion that capacity depends on rating conditions; it does not establish one hour rate as a universal industry standard.
A comparison table
A comparison table
When reviewing specifications or test reports, place the following information in one table: - Nominal capacity and its hour rate, such as C10 or C20 - Test temperature - Discharge cutoff voltage - Discharge method and current or power - Tested model, test object, and test basis If two products were evaluated under different conditions, pause the comparison and request complete discharge data or test notes for the relevant models. For short-duration, high-power applications, review the corresponding power-discharge information instead of extrapolating only from a long-duration Ah rating. A specification containing only one capacity figure should be traced to its discharge table, footnotes, or test description. Confirm the battery model and voltage platform, then read the row headings, column headings, and units. Manufacturers place hour-rate information in different locations. Copying the number alone can remove the condition that gives it meaning. Missing information should not be silently assumed. If one document states 25°C and the other gives no temperature, the second value cannot automatically be treated as if it used the same condition. The same principle applies when one report states a cutoff voltage and another lists capacity alone.
Nominal, laboratory and field data
Nominal, laboratory and field data
Nominal ratings, measured laboratory results, and equipment operating data answer different questions. A nominal value describes the product's rating basis. A laboratory report records the result for a specific sample under specified conditions. Field monitoring data are also affected by equipment load, environment, battery condition, and time in service. When these values appear in the same comparison, label their source and test date. A single field reading should not be used directly to redefine a product specification. Selection can then be divided into two questions: 1. What is the battery's rated value under its standard capacity-test conditions? 2. What current or power must the system deliver under the actual load? The first question supports document comparison. The second requires equipment requirements and application data from the battery manufacturer. The questions are related, but one Ah figure cannot replace the complete engineering calculation.
Separator validation
Separator validation
In an AGM lead-acid battery, the separator participates in electrolyte retention, ion transport, and the structural relationship within the plate group. Its specification and consistency should be evaluated against the target battery structure, manufacturing process, and test requirements. A single separator material property cannot be converted directly into complete-battery Ah capacity. It also cannot independently prove battery performance at C10, C20, or a specified power duty. Complete-battery capacity also depends on plate design, electrolyte, battery construction, assembly, and test conditions. Capacity conclusions must therefore come from tests on the relevant battery model under the relevant conditions. Viking Technology supplies AGM separators and supports specification discussions with battery manufacturers. Material matching should consider the target capacity-test condition, temperature, cutoff voltage, load method, separator thickness, and dimensions, with the final decision based on the specific battery design and validation results.
