Free tools

ENERGY TOOL · NO ACCOUNT REQUIRED

Battery runtime estimator.

Turn volts, amp-hours and real average watts into an estimated number of hours. See why standby loads matter.

Conceptual cutaway identifying cells, case and battery management. A nominal 12.8 V, 100 Ah example stores 1,280 Wh before usable-capacity and efficiency allowances. This is not a product teardown.
Slide the drawing sideways to read the full plate.
Inside a lithium house batteryConceptual cutaway identifying cells, case and battery management. A nominal 12.8 V, 100 Ah example stores 1,280 Wh before usable-capacity and efficiency allowances. This is not a product teardown.Reference: Dakota Lithium — internal BMS and battery use

INTERACTIVE CALCULATOR

Adjust the inputs. Estimates update instantly; nothing is uploaded.

YOUR ESTIMATE

Enter measurements to see the calculation.
How it works

Nominal energy = volts × amp-hours. Estimated runtime = nominal watt-hours × usable share × efficiency ÷ average load. This excludes many losses and battery-specific limitations.

Important limitation

Do not use this to size essential or emergency loads. The load may vary wildly; BMS, inverter idle draw, current limits, temperature and age all affect results.

IF YOU WANT THE WHOLE STORY

The math is the beginning.

LiFePO₄ can be a wonderful upgrade. It can also expose every shortcut in an old charging system. Do the checks in this order.

Read the companion guide

PUT THE RESULT TO WORK

Price a complete NG system, not a bare battery

Victron Lithium NG is a useful example of why the battery price is not the conversion price. It requires a compatible NG battery-management system. Engine charging may need a controlled DC-DC path, and a shunt monitor can make the energy budget visible. None of those components independently confirms that the boat is ready for lithium.

Read the buying guide →