Discharge curves

Battery discharge — pick a cell, the series/parallel arrangement, the starting charge, the cutoff voltage, and the temperature, then the load:
- constant current, or constant power (a load behind a DC-DC converter);
- a resistor;
- a pulsed load such as a radio or motor: a background current plus a pulse current at a duty cycle.
  
  The simulation steps the cell’s typical open-circuit voltage curve down as charge is drawn, subtracts the I·R drop of its internal resistance (which rises toward empty and in the cold), and applies Peukert’s law above the rated current. It stops at the cutoff, at empty, when a constant-power load collapses the voltage, or — for pulsed loads — when the dip during a pulse reaches the cutoff (a brownout). It reports runtime, delivered mAh and Wh, average voltage, heat lost in the cells, and, for constant current, the same pack at other C-rates.
Capacitor hold-up — time for a capacitor or supercapacitor to fall from its start voltage to the minimum under a constant-power load through a converter (t = C·(V₁² − V₂²)/(2P/η), integrated with ESR), constant current (t = C·ΔV/I), or a resistor (t = RC·ln(V₁/V₂)), and the capacitance needed for a required hold-up time — for saving data on power loss or riding out a brownout.
Bleeder resistor — time for a charged capacitor bank to fall to a safe voltage, the resistance for a required time, and the bleeder’s dissipation and rating.
Measured log — paste or open a CSV of time, voltage, and current (or give a constant current or load resistance) from a USB tester, an electronic load, or a microcontroller logger. You get capacity, energy, average voltage, and internal resistance from any current steps. Sample loads a simulated 18650 test with load pulses.

The cell data are typical figures for illustration — real cells vary by brand, age, and temperature, so check a datasheet’s discharge curves for anything that matters.

Share link copies a URL that opens this tool with your current settings — every value it remembers between visits, packed into ?s=. Opening a link replaces your saved settings for this tool. You can also write a short link by hand with cell (the cell preset), for example /tools/discharge/?cell=18650.

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