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Understanding how to read a lithium battery discharge curve and charging curve is essential for evaluating battery performance, optimizing device efficiency, and extending battery lifespan. These curves provide valuable insight into voltage behavior, internal resistance, capacity, temperature sensitivity, cycle life, and overall battery health.
In this guide, we break down everything you need to know—using clear explanations to help you analyze lithium battery curves like an expert.
A lithium battery discharge curve illustrates how the battery voltage changes over time or relative to parameters such as capacity, SOC (State of Charge), or DOD (Depth of Discharge). It is typically plotted as:
Voltage vs. Time
Voltage vs. Capacity
Voltage vs. SOC
Current vs. Time
Discharge curves reveal:
Battery stability and efficiency
Energy output at different C-rates
Voltage plateau behavior
Internal resistance characteristics
Available capacity under varying loads
These insights help engineers and users understand how a lithium battery behaves under real operating conditions.
The discharge rate (C-rate) significantly influences curve shape:
The curve declines gradually.
Voltage stays stable for a longer part of the discharge cycle.
Indicates higher usable capacity and energy efficiency.
The curve stays more stable but capacity appears lower.
Voltage drops faster due to increased internal resistance and heat.
Indicates reduced performance under heavy loads.
Understanding a discharge curve involves assessing multiple factors that indicate battery performance and overall health.
A flatter curve means:
Better voltage stability
Strong discharge performance
Improved energy delivery
The plateau indicates the battery’s ability to maintain stable voltage during most of the discharge process.
The area under the discharge curve correlates with the total dischargeable capacity.
A larger area = higher available capacity = longer runtime.
Internal resistance affects:
Voltage drop under load
Heat generation
Discharge efficiency
A battery with high internal resistance will show:
Faster voltage decline
Reduced power output
Notable sag at high loads
Internal resistance also increases with battery aging, making this curve a useful diagnostic tool.
By comparing discharge curves at different C-rates:
Lower C-rates show higher true capacity
Higher C-rates reveal losses due to polarization and internal resistance
This helps qualify batteries for high-power or long-endurance applications.
A healthy battery maintains a consistent discharge curve across cycles.
Signs of aging include:
Lower plateau voltage
Reduced capacity
Increased curve steepness
Comparing curves over time lets you predict lifespan and schedule replacements.
Several variables influence the shape and performance of a discharge curve:
Each chemistry has its own curve profile:
LiFePO4: Extremely flat plateau, stable output
LiCoO2: Higher energy density, steeper decline
LiMn2O4: Moderate voltage stability
Higher SOC = higher starting voltage.
Lower SOC = steeper voltage drop.
High C-rates increase voltage drop and reduce usable capacity.
Temperature affects electrolyte conductivity:
Low temperature → higher resistance, flatter curve
High temperature → improved performance but faster degradation
Aging increases internal resistance and decreases capacity, altering the curve significantly.
Material purity, electrode thickness, and production consistency impact discharge behavior.
Constant current → predictable curve
Constant power → faster voltage drop
Variable load → irregular curve shape
Higher impedance leads to greater voltage sag during discharge.
Electrolyte purity and additives influence ion mobility and voltage stability.
In battery packs, differences in parallel/series wiring affect discharge patterns.
Degraded batteries exhibit steeper declines and shorter plateaus.
A lithium battery charging curve shows how voltage and current change during the charging process. It includes three main phases:
Charger delivers a fixed current
Voltage rises steadily
Fastest charging phase
Voltage is held constant at the limit (e.g., 4.2V for Li-ion)
Charge current drops gradually
Battery approaches full capacity
Very low current
Maintains full charge
Prevents self-discharge
Understanding this curve ensures safe charging and avoids issues like overcharging that can damage the battery.
Comparing input energy and stored energy reveals how efficiently a battery charges.
High efficiency = less heat, longer lifespan.
This is the voltage at which the battery is considered fully charged.
Proper termination prevents:
Overcharging
Lithium plating
Capacity loss
Analysis ensures the battery charges within safe parameters.
It begins with a stable voltage plateau, followed by a gradual decline, ending with a steep drop at low SOC.
Higher C-rates steepen the curve and reduce available capacity.
It’s the region where voltage remains stable, indicating consistent power delivery.
Internal resistance rises as the battery empties, causing sharp voltage decay.
They are similar, though polymer cells may show slight variations due to construction.
Yes. Cold temperatures flatten the curve and reduce capacity significantly.
Monitoring them allows users to avoid deep discharges and high C-rate loads, improving longevity.
Edit by paco
Last Update:2025-11-21 09:59:39
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