Is sump pump battery runtime guaranteed?

No. Runtime changes with storm inflow, pump cycling, lift height, battery age, temperature, wiring losses, and charger health.

What duty cycle should I use for a sump pump?

Use several scenarios. A calm test may look like 10% duty cycle, while a severe storm may require 50% or more.

What else should I add besides a bigger battery?

Use a high-water alarm, regular testing, discharge checks, and a plan for long outages or fast inflow.

Planning tool

Sump Pump Battery Runtime Calculator

Estimate how long a backup sump pump battery may run using amp-hours, voltage, pump watts, efficiency, and pump duty cycle.

Estimated runtime Run the calculator

This estimate is for planning only. Real storm inflow, battery age, lift height, charger health, and pump cycling can change runtime.

Battery watt-hours: —
Effective pump load: —
Recommended planning buffer: Use at least 25% safety margin

Storm scenarios

Run more than one duty-cycle assumption

Light inflow10% duty cycle: useful for normal testing, not severe storm planning.

Active storm25% duty cycle: the default starting point for many homeowner comparisons.

Severe inflow50%+ duty cycle: stress-test whether battery-only backup is enough.

Before buying a bigger battery

Confirm pump wattage, float operation, discharge path, charger health, battery age, and whether the home needs a water alarm, generator plan, or secondary backup pump.

Compare backup systems

Related guides

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