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Battery Runtime Calculator

Estimate how long a battery bank will power a given load, based on battery capacity, voltage, depth of discharge and inverter efficiency - essential for sizing off-grid solar, RV and backup power systems.

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Result

Enter values above to calculate

These calculators provide estimates and educational results. Always verify critical engineering calculations against applicable standards and qualified professional review.

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What Is It

Battery runtime depends on more than just the amp-hour rating printed on the battery: depth of discharge (how much of the rated capacity can safely be used) and inverter conversion losses both reduce the energy actually available to the load.

How to Calculate

Enter the battery bank's capacity in amp-hours, its nominal voltage, the load it needs to power in watts, the battery chemistry (which sets a typical safe depth of discharge), and the inverter's efficiency. The calculator returns usable energy and expected runtime.

Example

A 100Ah, 12V lithium battery (80% usable depth of discharge) powering a 150W load through a 90% efficient inverter: usable energy = 100 × 12 × 0.8 = 960 Wh. Runtime = (960 × 0.9) / 150, about 5.8 hours.

Recommendations

Lead-acid batteries should generally not be discharged below 50% to preserve cycle life, while lithium batteries can typically handle 80-100% depth of discharge - using the wrong assumption for your battery chemistry will significantly overstate or understate real-world runtime.

Frequently Asked Questions

Why can't I use the full battery capacity?

Discharging a battery too deeply shortens its lifespan (especially lead-acid) or, for some chemistries, risks damage - manufacturers specify a maximum safe depth of discharge that this calculator applies to get a realistic usable energy figure.

Does load type (motors, electronics) affect runtime?

This calculator assumes a steady average load in watts; loads with high starting surges (motors, compressors) don't reduce total runtime by themselves but do require the inverter and battery to handle brief high-current spikes - see the Inverter Size Calculator for surge sizing.

Why does inverter efficiency matter?

An inverter converts DC battery power to AC and loses some energy as heat in the process - a 90% efficient inverter means 10% of the battery's usable energy never reaches the load, directly reducing runtime.

Last reviewed: 2026-09-12