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RV battery planning tool

RV battery runtime calculator: how long will your batteries run it?

Enter your battery bank, choose common RV loads, and see usable energy, estimated runtime, solar replacement watts, inverter needs and plain-English trip planning notes.

12V, 24V and 48V banksCPAP and fridge presetsSolar recharge estimate
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What it helps answer

  • Will my battery last overnight?
  • How long can I run a CPAP or 12V fridge?
  • How much solar would replace daily use?
  • Which loads are too large for my battery bank?
Interactive calculator

Start with the batteries you already have.

This calculator uses watt-hours so 12V lights, 120V inverter loads and lithium or lead-acid batteries can be compared in the same language.

Rated amp-hoursThe battery label number, such as 100Ah. Battery voltage changes how much energy that really is.
Usable capacityLithium can usually use more of its rating than lead-acid. The calculator leaves a practical reserve.
Watt-hoursWatts multiplied by time. A 50W device for 10 hours uses about 500Wh.
Inverter loss120V appliances use extra battery energy because the inverter is not 100% efficient.
Step 1

Battery bank

Choose a preset or enter the rated amp-hours of your full battery bank at the selected system voltage. Most travel trailers and fifth wheels are 12V unless they have a larger custom inverter system.

Step 2

Devices you want to run

Choose a preset or add your own devices. Check AC for household-style 120V items that run through an inverter. Check 24/7 for devices that run all day.

DeviceWattsQtyHours/dayAC24/7
Step 3 optional

Daily charging

Leave this at zero if you want a no-recharge runtime. Add solar or generator/shore charging if you want to see whether the battery can keep up across multiple days.

How to read the result

Battery runtime is really a watt-hour problem.

A 100Ah 12V battery and a 100Ah 24V battery do not store the same energy. Multiply volts by amp-hours to compare them fairly. Then reduce that number by the usable percentage for the battery type.

Why lead-acid and lithium results differ

Lead-acid batteries are commonly planned around about half of their rated capacity because deep discharges shorten life and voltage sags under load. LiFePO4 batteries can usually deliver more usable energy, but the battery management system, temperature limits and charger settings still matter.

Why AC appliances drain batteries fast

A microwave, coffee maker, electric heater or hair dryer may only run briefly, but it pulls a large amount of power while it is on. The inverter also loses energy converting battery power to 120V AC power.

When solar changes the answer

Solar does not make a battery larger; it replaces energy during the day. If daily charging is greater than daily use, the setup may keep up in good sun. If charging is less than use, the battery still trends downward.

Battery runtime FAQ

Common RV battery sizing questions.

How many amp-hours do I need for boondocking?

Start with daily watt-hours, add a reserve, then choose enough usable battery capacity for the number of days you want without good charging.

Can I run an RV air conditioner from batteries?

It is possible with a large lithium bank, strong inverter, heavy cabling and charging plan, but it is far beyond a typical small battery setup.

Why does my battery die faster than the math says?

Common causes include old batteries, hidden loads, inverter idle draw, voltage drop, cold temperatures, optimistic appliance ratings and less solar than expected.