RV battery and solar calculator: energy and reserve

Estimate battery capacity for a chosen no-charge period and solar energy for stated conditions. Keep daily amp-hours and the energy conversion at the same bank voltage. The usable percentage is a planning allowance, not a universal chemistry limit or a charging-safety check.

Daily battery consumption measured at the bank voltage entered below. Include inverter and standby losses.

Use the actual documented value for the intended operating conditions.

Selects a default allowance only; it does not determine product safety or charging compatibility.

Use the actual documented value for the intended operating conditions.

Equivalent full-sun hours for the location and season, not daylight hours. Zero is allowed.

Your assumed total delivered-energy loss percentage, not a universal industry figure.

The voltage used for all Wh-to-Ah conversion in this example. Replace 12.8 V if your documented basis differs.

Optional product-specific planning allowance. Blank uses 50% for flooded/AGM or 80% for lithium; these are chosen defaults, not physical cutoffs.

The energy estimate runs in your browser with JavaScript enabled. Otherwise, submitting battery and load values returns the equivalent calculation from this site.

The defaults are assumptions you can replace

The tool uses 50% for flooded/AGM and 80% for lithium unless you enter another usable allowance. Trojan’s maintenance guidance recommends shallower discharges for service life; it does not establish a physical 50% cutoff for every battery. Obtain the actual product’s capacity and operating restrictions.

A default four sun hours or 25% loss is not a year-round forecast. PVWatts documents a different 14% system-loss default, with inverter and temperature treatment separate. Assess the location, season, shading and complete charging path rather than copying a default.

Calculate capacity and replacement energy separately

For 60 Ah daily use, two days without charging and an 80% chosen allowance, the nominal bank calculation is 60×2÷0.8=150 Ah. At 12.8 V, the daily energy use is 768 Wh. An assumed 400-W array for four sun hours with 25% losses yields 1200 Wh, or 93.75 Ah at that same voltage.

Assumed 1200 Wh daily solar outputDaily use: 768 Wh; Remaining estimated energy: 432 WhAssumed 1200 Wh daily solar outputDaily use: 768 WhRemaining estimated energy: 432 Wh

The estimated surplus is 33.75 Ah before any losses absent from the chosen allowance. It is not a weather guarantee or proof that a particular controller can accept the array. At zero sun, the output is zero and no finite array breaks even in that scenario.

Choose from energy rather than a package labelMeasure daily consumption at a documented voltageThen: Choose usable reserve and no-charge durationThen: Check solar balance and another charging optionChoose from energy rather than a package labelMeasure daily consumption at a documented voltageChoose usable reserve and no-charge durationCheck solar balance and another charging option

Size does not establish charging compatibility

The Victron Lithium Smart manual permits charging only within its specified temperature range, including a+5°C lower limit for that product. Do not substitute a universal freezing cutoff or assume every battery has an internal heater or disconnect.

This calculation does not design wiring, protection, inverter startup or mounting. Inputs stay on the device during script calculation; the fallback submits them to this site. Use controller and array limits before buying equipment.