RV Battery Days of Autonomy Calculator

Estimate how many off-grid days your RV battery bank can support after usable depth of discharge, battery age, temperature, inverter losses, DC loads, AC loads, solar harvest, driving charge, generator charge, and reserve margin.

🏕RV Battery Autonomy Presets

⚙Battery Bank, Loads, Charging, and Reserve Inputs

Nominal battery bank voltage Use the nominal DC voltage of the house battery bank.

Battery chemistry and usable range Lithium and lead-acid banks should not use the same usable depth.

Custom usable battery percentage Use battery manufacturer guidance if it differs from the presets.

Number of batteries in the bank Count batteries that are part of the same house bank.

Rated amp-hours per battery For a matched bank, use the label Ah rating of one battery.

Battery age and health factor Accounts for capacity fade, imbalance, and real-world battery condition.

Battery temperature during use Cold batteries deliver fewer usable watt-hours, especially lead-acid banks.

Protected reserve target Reserve is kept after usable capacity, so it reduces planned autonomy.

Average DC appliance load in watts Use average watts for fridge controls, lights, fans, pump, detectors, and USB.

DC appliance hours per day For always-on loads, enter 24 hours at their average watt draw.

Average AC inverter load in watts Laptops, TV, CPAP power brick, microwave use, and other 120 V loads.

AC inverter load hours per day Inverter losses are applied to this energy separately from DC loads.

Inverter efficiency AC watt-hours are divided by this efficiency before battery draw.

Inverter standby watts Idle inverter draw when left on without a major AC load.

Inverter standby hours per day Turn the inverter off in the model if you shut it down between uses.

Always-on parasitic DC watts Propane detector, battery monitor, radio memory, control boards, and relays.

Furnace blower amp draw Set to zero in warm weather. Many RV blowers draw 3 to 10 amps.

Furnace blower hours per day Use actual run-time hours, not the hours the thermostat is enabled.

Solar array size in watts Panel nameplate watts on the RV, portable array, or both combined.

Usable peak sun hours per day Use a winter or cloudy-season value when planning a cautious stay.

Solar system harvest efficiency Includes controller loss, heat, wiring, angle, and light shade.

Cloud or shade derate Applied after sun-hours and system efficiency.

Alternator or DC-DC charge amps Average house-bank charge current while driving, after DC-DC limits.

Driving charge hours per day Use zero for stationary camp days.

Generator or shore charger amps Average DC charging amps delivered into the house bank.

Generator or shore charger hours per day Set both generator fields to zero for silent battery-only autonomy.

Estimated autonomy

0.0

days before reserve

Usable battery

0 Wh

after chemistry, age, temperature, and reserve

Net daily draw

0 Wh

loads minus daily charging

Daily charging help

0 Wh

solar plus driving and generator charging

📊Battery Planning Spec Grid

Volts times amp-hours gives battery energy

90%

Typical LiFePO4 planning depth before reserve

50%

Common lead-acid planning depth before reserve

0.90

Common pure sine inverter efficiency factor

24 hr

Parasitic loads run all day in the model

70%

Typical roof solar harvest planning factor

10-25%

Reserve range for cautious RV battery planning

1 kWh

Equals 1,000 watt-hours of battery energy

📋RV Battery Reference Tables

Battery type	Usable band	Cold effect	Planning note
LiFePO4 lithium	80 to 90%	Moderate discharge derate	Great usable capacity, but charging below freezing needs protection.
AGM lead acid	45 to 55%	Noticeable cold loss	Good sealed option, but deep cycling shortens life.
Flooded lead acid	40 to 50%	High cold and voltage sag	Use conservative depth and check state of charge carefully.
Gel lead acid	50 to 60%	Moderate cold loss	Charge settings must match the battery specification.

Daily load	Typical draw	Hours	Daily energy
LED lights and USB	15 to 35 W	4 to 6	60 to 210 Wh
Compressor fridge	35 to 60 W average	8 to 16	280 to 960 Wh
Furnace blower	3 to 10 A	1 to 8	36 to 960 Wh at 12 V
CPAP or laptop	40 to 120 W AC	2 to 8	90 to 1,070 Wh after inverter loss

Charging source	Formula	Efficiency cue	Best use
Roof solar	Watts x sun hours x harvest	50 to 80%	Daily offset during stationary camping.
Portable tilted solar	Watts x sun hours x harvest	70 to 88%	Better angle and shade avoidance.
DC-DC alternator	Volts x amps x drive hours	85 to 95%	Reliable help on travel days.
Generator charger	Volts x amps x run hours	80 to 95%	Fast recovery when solar is weak.

Bank example	Raw capacity	Planned usable	Autonomy cue
One 12 V 100 Ah LiFePO4	1,200 Wh	About 1,080 Wh	Light overnight or careful weekend.
Two 12 V 100 Ah AGM	2,400 Wh	About 1,200 Wh	Good for modest loads without big AC use.
Two 12 V 200 Ah LiFePO4	4,800 Wh	About 4,320 Wh	Multi-day fridge, fan, CPAP, and laptop use.
Four 12 V 100 Ah LiFePO4	4,800 Wh	About 4,320 Wh	Large trailer or fifth wheel house bank.

💡Battery Autonomy Tips

Separate AC and DC energy: Direct DC loads use battery watt-hours directly, while inverter loads need extra battery energy because the inverter is never 100% efficient.

Plan from the weakest day: For cold or shaded trips, use the lowest expected solar harvest and include furnace blower hours before trusting a multi-day result.

Battery autonomy show how many days a battery bank can supply power to the RV’s electrical loads without receiving a charge from an outside source. Battery autonomy is a critical measurement to determine if the lights in the RV will function and if the RVs furnace will function during the trip. In order to calculate the battery autonomy for an RV trip, you must calculate the total capacity of the battery bank and the total electrical load consumption.

The first step in calculating battery autonomy is to determine the usable capacity of the battery bank. You can determine the total capacity of an battery bank by multiplying the voltage of the battery bank by the amp-hour capacity of the battery bank. However, not all battery bank have the same total capacity.

How Long Your RV Battery Will Last

The chemistry of the batteries within the battery bank determine how much energy can be drawn from the battery bank. Additionally, the age of the battery bank impact the usable capacity of the battery bank. Battery banks wear down over times.

Finally, the temperature of the battery bank impacts the usable capacity of the battery bank. Battery banks has reduced capacity to deliver energy in cold temperatures. The second step in calculating battery autonomy is to determine the electrical load that will drain the battery bank of its energy.

Electrical loads can come from the RV’s direct DC devices or its AC devices. The direct DC device that are typically powered by the battery bank include lights and water pumps. The AC devices require an inverter to be use to power the devices.

The inverter will use additional energy from the battery bank to perform the necessary conversions of DC to AC power. Additionally, some electrical loads will use energy from the battery bank for extended periods of time, like the furnace blowers. Other device, like propane detectors, will create parasitic draws on the battery bank.

The third step in calculating battery autonomy is to calculate the charging source of the battery bank. The charging sources can include solar panels, alternators, or generators. The size of the solar panel array installed on the RV and the amount of sunlight that hits those panels affects the energy provide by solar panels.

An alternator or DC-DC charger will provide energy while the RV is driven. Finally, a generator will provide energy more quick than solar panels will in cloudy weather. In addition to the factors described above, temperature also plays a critical role in battery autonomy.

Battery autonomy calculations is based on the capacity of lead-acid battery banks to be reduced in cold temperatures, as well as the likelihood that the lithium battery banks will not be able to accept a charge in cold temperatures. Therefore, it is necessary to plan for battery autonomy according to the lowest temperatures that will be experienced during the trip, and for the shortest period of sunlight during the trip. Planning according to the lowest temperatures will ensure that the RV is not surprised by rapidly diminish battery autonomy during the trip.

The reader can reference a set of tables to check the calculations of the energy that will be used by the RV’s electrical loads, as well as the energy that will be provide by the charging sources. These tables will assist the reader in checking the calculations, but not as fixed values. For instance, the time that each person use a laptop will vary between RV travelers.

When calculating battery autonomy, there are some mistake to avoid. One mistake is to not account for the fact that an inverter left on standby will use more energy than the actual loads that are running on the RV. Another mistake is not to properly calculate the reserve capacity of the battery bank.

For instance, a small change in the use of the RV’s furnace or in the use of the inverter will have a more greater impact on battery autonomy than adding more solar panels to the RV. Finally, battery autonomy calculators are used to provide people with an understanding of the different factor that impact battery autonomy. For instance, a person can choose an RV with a small battery bank if they plan to go on a short trip, or they can choose a larger battery bank for their RV if they plan to travel long distance.

All the calculator must do is perform the calculations for the users once they have entered the number of electrical loads that the RV will have and the assumptions about the charging of the battery bank.

RV Battery Days of Autonomy Calculator