Battery Discharge Curve Animation

Watch battery voltage, usable capacity, cutoff margin, and runtime change as an IoT device discharges.

A beginner-first battery discharge workbench with chemistry scenarios, animated voltage curves, Peukert and temperature derating, cutoff warnings, and practical IoT design feedback.

Animation Beginner first Battery curves IoT power design

Battery Discharge Curve Animation

Move through a battery discharge and watch the voltage curve, knee region, usable capacity, cutoff margin, and runtime estimate change together.

3.86 V present battery voltage

21.1 h remaining runtime estimate

+0.86 V margin above cutoff

2600 mAh usable derated capacity

Goal

See why a battery can look healthy for hours and then drop quickly near the end.

Try First

Press Play, then raise the load current and watch how runtime and usable capacity change.

Watch

The orange knee band is the danger area. A design should usually stop before this region.

Why It Matters

IoT nodes often fail when firmware trusts voltage alone or uses the full rated capacity.

Controls

Choose a chemistry, set the load and environment, then step through the discharge curve.

Chemistry 1-cell rechargeable

View voltage curve

Playback manual

State of charge 70% 100% is full. 0% is empty. The dot on the graph shows this point.

Average load 80 mA Use average current after duty cycle, sleep current, and radio bursts are combined.

Temperature 22 C Cold cells usually deliver less usable capacity, especially at high load.

Cutoff voltage 3.00 V Set the firmware or power supervisor threshold before the unsafe low-voltage region.

1. Full High open-circuit voltage, but little has been learned about runtime yet.

2. Plateau Voltage changes slowly, so voltage-only state of charge is weak.

3. Knee Voltage begins falling fast and remaining energy is hard to trust.

4. Cutoff The device should stop, save state, or request service.

5. Brownout Running below cutoff can reset electronics or damage some cells.

Plateau current discharge region

20% SoC approximate knee begins

100% capacity retained after load and temperature

92% rated capacity usable before cutoff

Voltage Curve

The dot moves left to right as stored energy is used. The shaded area marks the knee where voltage falls quickly.

Safe plateau

Reading: This point is still above cutoff, but the runtime estimate depends more on load current than voltage.

Live Calculation

Li-ion has a sloped-to-flat discharge curve and a clear end-of-life knee near low state of charge.

Voltage and cutoff

Battery voltage3.86 V

Cutoff threshold3.00 V

Voltage margin+0.86 V

Runtime estimate

Nominal capacity2600 mAh

Derated capacity2600 mAh

Remaining runtime21.1 h

Design flags

Use a fuel gauge or coulomb counting if the application needs accurate remaining-capacity estimates.

Voltage Check

Voltage is still comfortably above the configured cutoff threshold.

+0.86 V margin

Runtime Check

Runtime is calculated from derated capacity divided by average current.

21.1 h remaining

Battery Fit

This chemistry is a good teaching fit for rechargeable, medium-current sensor nodes.

Good IoT fit

Beginner Ramp

A discharge curve shows battery voltage as stored energy is used. It is not a straight fuel gauge.

• State of charge: how much energy remains, shown as a percentage.
• Cutoff voltage: the point where the device should stop drawing power.
• Knee: the late part of the curve where voltage falls quickly.

Chemistry Map

Different cells have different voltage shapes, safety limits, and load behavior.

• Li-ion: high energy, common in rechargeable devices, needs protection.
• LiFePO4: safer and flatter voltage, but voltage-only SoC is harder.
• NiMH: robust AA rechargeable cells with moderate high-load derating.
• Alkaline: convenient disposable cells, but capacity falls sharply at high current.

Knee Region

The knee is where a small amount of remaining capacity can cause a large voltage drop.

• Set cutoff before the electronics brown out.
• Save data before entering the knee if the device stores readings locally.
• Do not promise long remaining runtime just because voltage looked stable earlier.

Formula Reference

The basic runtime estimate is:

runtime hours = usable capacity mAh / average current mA

The animation also uses a simple Peukert-style teaching derate:

C effective = C nominal x (I rated / I actual)^k-1

This is a simplified design estimate, not a replacement for cell datasheet testing.

Temperature Note

Cold batteries usually provide less usable capacity because internal resistance rises and voltage sags more under load.

• Outdoor sensors should be tested at the coldest expected temperature.
• High load plus cold temperature is a common cause of unexpected reset.

Practical IoT Note

For reliable deployments, estimate runtime conservatively and test with the real radio duty cycle.

• Use average current for lifetime math, but check peak current for voltage sag.
• Leave margin for aging, self-discharge, temperature, and manufacturing variation.

Practice 1

Set LiFePO4, move SoC from 90% to 40%, and notice why voltage changes very little.

Practice 2

Select alkaline, raise load above 300 mA, and explain why the rated mAh is no longer realistic.

Practice 3

Lower the cutoff voltage and decide whether the extra runtime is worth the brownout risk.

Related Study

Battery Life Calculator Turn current draw and duty cycle into lifetime estimates. Power Budget Calculator Compare device states and find the biggest current cost. Energy Harvesting Cycle See when harvested energy can refill or sustain a battery.