Depth of Discharge (DoD) Calculator
Convert between depth-of-discharge (DoD) and state-of-charge (SoC), compute the Ah or Wh consumed at a given DoD, and estimate cycle life for Li-ion, LiFePO4, lead-acid, and NiMH chemistries.
How to Use
- Enter the depth of discharge as a percentage (0% = full charge, 100% = fully drained).
- Enter battery capacity (Ah or Wh — the tool works in whichever unit you use).
- Pick the chemistry. The cycle-life estimate at that DoD uses published chemistry-specific curves.
- Results show complementary SoC, charge used, charge remaining, and estimated cycles before 80% capacity loss.
Show Work
Formulas
History of DoD and Cycle-Life Analysis
Depth-of-discharge as a rated parameter entered engineering practice with lead-acid stationary batteries in the early 1900s. Telegraph and telephone exchanges needed batteries that could reliably deliver power for years; operators noticed that cells routinely discharged to empty failed in months, while cells used only to 50% lasted a decade or more. Formal DoD/cycle-life curves were first published by Exide and Varta in the 1930s as part of battery datasheets for telecom and utility applications.
The logarithmic dependence of cycle life on DoD — roughly a 2× increase in cycles for every 10% reduction in DoD — was characterized in detail during WWII for submarine lead-acid banks and the emerging US Navy battery program. The same relationship held, with chemistry-specific coefficients, for the nickel-cadmium cells that followed in the 1950s, and again for nickel-metal-hydride and lithium-ion as each chemistry was commercialized in the 1990s and 2000s.
Today every major battery manufacturer publishes cycle-life vs. DoD curves, and every serious Battery Management System uses a programmable DoD cutoff to enforce the design trade-off between capacity utilization and lifetime. Tesla, BYD, LG Chem, CATL, and Panasonic all ship battery datasheets with these curves plotted — and this calculator's cycle-life estimates come from typical published values for each chemistry.
About This Calculator
Enter a target DoD percentage, battery capacity, and chemistry. The tool returns the complementary State of Charge, the capacity withdrawn at that DoD, capacity remaining, and an estimated cycle count before the battery reaches 80% of its original capacity (the industry-standard "end of life" threshold).
The cycle estimates use typical published curves for each chemistry; real-world cycle life also depends on temperature, charge rate, and rest time between cycles. All math runs client-side; no values leave your browser.
Frequently Asked Questions
What's the difference between DoD and SoC?
They\'re complementary — DoD + SoC = 100%. State of Charge (SoC) is how much energy remains; Depth of Discharge (DoD) is how much has been removed. If you\'ve used 30% of the pack, DoD = 30% and SoC = 70%. Most consumer battery meters display SoC; engineers and battery management systems typically work in DoD.
Why limit DoD?
Deep cycles wear batteries nonlinearly. Li-ion cycled to 100% DoD lasts ~500 cycles before dropping to 80% capacity; cycled only to 50% DoD it lasts ~1500 cycles — three times longer for half the daily capacity. The math strongly favors oversizing the pack and using less of it per cycle.
Which chemistries tolerate deep discharge?
LiFePO4 is the champion — 80–90% DoD daily for 2000+ cycles. Li-ion handles 80% DoD for moderate cycle counts. Lead-acid permanently degrades past 50% DoD. NiMH tolerates 80–90% DoD for 500–1000 cycles. Alkaline (primary) is single-use and fine to drain completely.
How does BMS firmware enforce DoD limits?
Every battery management system has a low-voltage cutoff that triggers at the cell voltage corresponding to the configured maximum DoD. For a Li-ion pack set to 80% DoD max, the BMS cuts off at roughly 3.0 V/cell, leaving ~20% capacity in reserve. The reserve isn\'t wasted — it\'s the cycle-life insurance premium.
Can I charge to 100% SoC every time?
You can, but you\'ll pay in cycle life. Li-ion batteries also age faster at high SoC; Tesla and other EV makers recommend charging only to 80% for daily driving, reserving 100% for road trips. The math is symmetric — reducing time at the voltage extremes (high or low) extends life.
Common Use Cases
EV Daily Charging
Leaving an EV plugged in and charging to 80% SoC daily extends battery life roughly 3× compared to 100% SoC daily cycling. Most manufacturers recommend this explicitly.
Solar Off-Grid Sizing
LiFePO4 banks sized for 80% usable capacity give long cycle life and predictable runtimes. Lead-acid systems require 2× the nameplate capacity to safely deliver the same usable energy at 50% DoD.
Phone / Laptop Longevity
Limiting charge to 80% (via "charge limit" features in iOS/Android/macOS) and avoiding full discharges can double battery lifespan — often outlasting the device itself.
UPS Battery Replacement Planning
A UPS cycling lead-acid to 80% DoD during every outage will need replacement batteries within 2 years; limiting to 50% DoD extends replacement intervals to 4+ years.
Grid-Scale Storage
Utility-scale BESS installations target 70–80% DoD to meet 10-year warranty life. The remaining 20–30% is deliberate reserve, not idle capacity.
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