Marine Lithium Battery Calculators
Free formulas for boat battery sizing, inverter current, solar output, runtime, alternator charging and energy balance.
Battery energy
Wh = V x Ah
kWh = V x Ah / 1000
Appliance energy
Wh/day = watts x hours/day x duty cycle
Approximate inverter DC current
DC amps = AC watts / (battery voltage x inverter efficiency)
Bank size from daily energy
Nominal bank Wh = daily Wh x autonomy days / planned usable fraction
Solar planning
Solar Wh/day = panel watts x peak-sun-hours x system factor
Approximate recharge time
Hours = Wh to replace / effective charger watts
DC charger watts
Approximate watts = charging voltage x charging amps
Watermaker efficiency
Wh/L = operating watts / litres per hour
Generator recovery
Generator hours = energy deficit / effective battery-charge power
Every calculator should show a warning that actual product limits and real measurements override generic formulas.
Apply this guidance to your boat
Use this page as one input to a vessel-specific plan. Record the actual equipment, cable runs, charging sources and operating pattern aboard before choosing hardware or changing the installation.
- Measure the real load and its operating time instead of relying on a label or a generic boat profile.
- Check every proposed current against the battery, BMS, protection, cable and connection limits.
- Confirm the result against current manufacturer instructions and the rules that apply to your vessel.