How to Estimate Battery Runtime Based on Depth of Discharge (DoD)
The Depth of Discharge (DoD) Runtime Calculator helps you estimate how long a battery can power your devices or loads before reaching its usable limit. Depth of discharge refers to the percentage of total battery capacity that has been used. A 100% DoD means the battery is completely drained, while 50% DoD means half of its energy has been consumed.
In real-world solar and off-grid systems, running a battery down to 100% discharge is never recommended. Batteries are rated for a limited number of charge–discharge cycles, and deeper discharges significantly shorten their lifespan. For example, lead-acid batteries often last 500 cycles at 50% DoD, but only around 200 cycles at 80% DoD. Lithium-ion batteries (Li-ion or LiFePO₄) can safely reach higher DoD levels, typically 80–90%, without severe degradation.
Understanding the Runtime Formula
The calculator uses this formula:
Runtime (hours) = (Battery Voltage × Capacity × DoD × Inverter Efficiency × (1 − Safety Margin)) ÷ Load Power
This formula considers your battery’s voltage and capacity (in amp-hours), the load power (in watts), inverter efficiency losses, and an optional safety margin to avoid full discharge. It provides a realistic estimate of how many hours your battery can sustain a given load before reaching the set depth of discharge.
Recommended Depth of Discharge Settings
- Lead-acid batteries: 50% DoD recommended to prevent sulfation and extend life.
- Lithium-ion batteries: 80% DoD typical for balanced lifespan and performance.
- LiFePO₄ batteries: Up to 90% DoD usable safely in most systems.
Example Calculation
Suppose you have a 200Ah, 12V LiFePO₄ battery with an inverter efficiency of 90% powering a 300W load, and you set your usable DoD to 80% with a 10% safety margin:
Runtime = (12 × 200 × 0.8 × 0.9 × 0.9) ÷ 300 = 5.18 hours
That means your system can continuously power a 300W load for about 5.2 hours before reaching the safe depth of discharge.
Practical Tips for Longer Battery Runtime
- Reduce unnecessary loads and optimize inverter efficiency.
- Use higher voltage systems (24V or 48V) for better efficiency with the same power output.
- Avoid frequent deep discharges to preserve battery health.
- Ensure batteries are kept in moderate temperatures (20–30°C).
Conclusion
Understanding how Depth of Discharge affects runtime helps you design a more reliable and efficient off-grid or backup power system. By balancing discharge depth, inverter efficiency, and safety margin, you can maximize both performance and lifespan. Use this calculator to plan your daily energy usage and choose the right battery capacity for your application.
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