PowerCalcLab

Battery calculator

RV Battery Bank Calculator

Build an RV house-battery budget without applying inverter losses to native 12 V or 24 V loads. The result includes nominal kWh, Ah and a rounded whole-battery layout.

Advanced assumptions

Results update as you type. The calculator runs entirely in your browser — nothing you enter is sent anywhere.

Minimum nominal RV battery bank3.14 kWh · 245 Ah

Calculation breakdown

Daily battery-side energy1,104 Wh/day
AC energy at battery444 Wh/day
Whole-battery layout1S × 3P = 3
Installed nominal bank3.84 kWh · 300 Ah
Bank Wh = [(daily DC Wh + daily AC Wh ÷ inverter efficiency + parasitic Wh) × days × margin] ÷ DoD ÷ health
= [(600 + 400 ÷ 0.9 + 60) × 2 × 1.15] ÷ 0.9 ÷ 0.9
= 3.14 kWh = 245 Ah at 12.8 V
  • DC and AC daily loads are separated so inverter loss is applied only to the AC energy budget.
  • The whole-battery layout rounds capacity up; verify manufacturer limits before series or parallel connection.

Before you rely on this

Verify battery series/parallel permissions, BMS and fault-current limits, alternator protection, cable and fuse sizing, ventilation and RV installation requirements.

Method

How the number is reached

Daily DC loads go directly into the battery energy budget. Daily AC energy is divided by inverter efficiency first, then always-on controls and monitoring loads are added.

The off-grid energy is increased by a design margin and divided by usable depth and end-of-design health. Ah is based on nominal bank voltage, and whole modules are rounded up after series voltage is established.

Battery Wh/day = DC Wh/day + AC Wh/day ÷ inverter efficiency + parasitic Wh/day
Nominal bank Wh = battery Wh/day × days × margin ÷ DoD ÷ health
Bank Ah = nominal Wh ÷ nominal bank voltage

Symbols

DoD
Allowed depth of discharge
S/P
Series batteries / parallel strings

Worked examples

The same maths, applied

Example

Two off-grid days with mixed 12 V and AC loads

The RV uses 600 Wh/day of DC energy, 400 Wh/day of AC energy through a 90% efficient inverter, and 60 Wh/day of parasitic energy. The LiFePO4 design uses 90% DoD, 90% health and 15% margin.

Battery energy/day = 600 + 400 ÷ 0.90 + 60 = 1,104.4 Wh
Design energy = 1,104.4 × 2 × 1.15 = 2,540.2 Wh
Nominal bank = 2,540.2 ÷ 0.90 ÷ 0.90 = 3,136.1 Wh
Capacity = 3,136.1 ÷ 12.8 = 245 Ah

Result: 3.14 kWh · 245 Ah; three 12.8 V 100 Ah batteries in parallel.

Limits of the model

What it assumes, and where it stops

Assumptions

Daily energy estimates represent real duty cycles and no charging is credited during the off-grid period.

Not covered

Does not size alternator, shore charger, solar array, inverter power, BMS current, conductors or fuses.

Sources

Where these figures come from

  • How to Size a Solar System for Your RVVictron EnergyManufacturer sizing walkthrough connecting daily energy, days of autonomy, system voltage and chemistry-dependent usable capacity, with an explicit reminder to include inverter losses.
  • Wiring Unlimited — Battery bank wiringVictron EnergyManufacturer guidance for series, parallel and series/parallel battery banks, balanced current paths and connection safety.
  • Inverter Smart — Technical specificationsVictron EnergyManufacturer ratings that distinguish continuous watts, continuous VA, temperature derating, peak power, maximum efficiency and zero-load consumption.

Next steps

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Last meaningful update: 2026-08-19. This date changes only when the model, the sources or the guidance change.