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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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The capacity of a lead-acid cell is measured in
amperes
ampere-hours
watts
watt-hours
ampere-hours
Quick Summary: The capacity of a lead-acid battery is defined as the total amount of charge it can deliver under specific discharge conditions, measured in ampere-hours (Ah). It represents the product of the discharge current in amperes and the time in hours for which the battery can sustain that current until it reaches a specified cut-off voltage.
The capacity of a lead-acid battery is defined as the total amount of charge it can deliver under specific discharge conditions, measured in ampere-hours (Ah). It represents the product of the discharge current in amperes and the time in hours for which the battery can sustain that current until it reaches a specified cut-off voltage.
C=I×t — where C is capacity in Ah, I is current in Amperes, and t is time in hours.
Cp=Ik×t — Peukert's law formula showing the effect of discharge rate on capacity.
The chemical energy stored within the lead-acid plates is converted into electrical energy during discharge. The capacity is governed by the Peukert's law, which states that the available capacity of a battery decreases as the discharge current increases. Thus, a fixed Ah rating is always specified at a particular discharge rate (e.g., 20-hour rate).
Ampere-hour (Ah) is the standard industry unit for electrochemical energy storage capacity.
The rated capacity is temperature-dependent and decreases as ambient temperature drops.
A battery rated at 100Ah can theoretically provide 5A for 20 hours.
Actual capacity depends on the discharge rate; higher discharge rates lead to lower effective Ah capacity.
Standardized metric for comparing different battery models.
Provides a direct indication of expected runtime for known loads.
Does not account for voltage sag under load, which defines the 'usable' energy.
Requires specifying discharge time (e.g., C20) to be accurate due to non-linear behavior.
Automotive starter batteries.
Uninterruptible Power Supply (UPS) systems.
Solar photovoltaic storage banks.
Watts (W) represent power, and Watt-hours (Wh) represent total energy (Capacity × Voltage).
Amperes (A) measure instantaneous current flow, not total storage capacity.
B is correct — The capacity of a battery is defined as the total charge delivery capability, which is the product of current and discharge time, expressed in ampere-hours (Ah).
Always check the discharge rate (e.g., C10 vs C20) in datasheets; a higher Ah rating at a slow discharge rate may provide less real-world runtime under high-current conditions compared to a lower Ah battery with better Peukert performance.