RV Battery Size Calculator
Estimate the amp-hours and watt-hours needed for your RV, with usable capacity, battery voltage and reserve explained.
Compare Current OptionsThe mistake in many RV battery estimates is treating “100Ah” as a fixed amount of usable power regardless of chemistry or voltage. Capacity is energy: nominal watt-hours equal amp-hours multiplied by battery voltage. A 12.8V lithium battery rated 100Ah stores approximately 1,280Wh nominally; the energy you plan to use depends on your chosen reserve, manufacturer guidance and inverter losses.
As an Amazon Associate, we earn from qualifying purchases.
01 Three realistic load profiles
Illustrative calculations help you check whether your inputs are plausible. They are not product rankings or claims that all RVs in a category use the same power.
One day at 80% usable capacity: about 59Ah nominal. This is an illustration, not a universal recommendation.
Two days at 80% usable capacity: about 293Ah nominal. This is an illustration, not a universal recommendation.
Two days at 80% usable capacity: about 586Ah nominal. This is an illustration, not a universal recommendation.
02 Battery sizing examples
These examples use 12.8V LiFePO4, 80% planned usable capacity and the stated days of autonomy, without an extra reserve margin.
| Use case | Daily load | Nominal battery estimate | What to check |
|---|---|---|---|
| Light weekend loads | 600 Wh/day | One day at 80% usable capacity: about 59Ah nominal | A small fridge, LED lights and electronics can vary dramatically; measure the actual energy use. |
| Moderate off-grid loads | 1,500 Wh/day | Two days at 80% usable capacity: about 293Ah nominal | Fridge duty cycle, inverter standby and cloudy-day solar shortfalls can dominate. |
| Heavy inverter use | 3,000 Wh/day | Two days at 80% usable capacity: about 586Ah nominal | Air conditioning and cooking can make a battery-only plan expensive; peak inverter current matters. |
03 Understand the worked numbers
The following examples show how changes in load and autonomy affect required capacity; use your own measurements for final sizing.
Light weekend loads
One day at 80% usable capacity: about 59Ah nominal.
Assumption: This example uses the specified daily consumption and 80% planned usable depth of discharge. The battery voltage is 12.8V, not the 120V AC outlet voltage.
What changes the answer: A small fridge, LED lights and electronics can vary dramatically; measure the actual energy use.
Your measured daily energy use is near 600 Wh/day.
Peak loads, low-temperature charging, solar recovery, or system wiring have not been assessed.
Moderate off-grid loads
Two days at 80% usable capacity: about 293Ah nominal.
Assumption: This example uses the specified daily consumption and 80% planned usable depth of discharge. The battery voltage is 12.8V, not the 120V AC outlet voltage.
What changes the answer: Fridge duty cycle, inverter standby and cloudy-day solar shortfalls can dominate.
Your measured daily energy use is near 1,500 Wh/day.
Peak loads, low-temperature charging, solar recovery, or system wiring have not been assessed.
Heavy inverter use
Two days at 80% usable capacity: about 586Ah nominal.
Assumption: This example uses the specified daily consumption and 80% planned usable depth of discharge. The battery voltage is 12.8V, not the 120V AC outlet voltage.
What changes the answer: Air conditioning and cooking can make a battery-only plan expensive; peak inverter current matters.
Your measured daily energy use is near 3,000 Wh/day.
Peak loads, low-temperature charging, solar recovery, or system wiring have not been assessed.
04 Seven critical sizing checks
Battery energy capacity is only one part of a safe and reliable RV electrical system.
- Measure watt-hours rather than guessing amp-hours: Multiply each device’s watts by daily run hours; include DC loads and AC loads through an inverter.
- Choose nominal battery-bank voltage: Enter the actual bank voltage: 12.8V for many 12V LiFePO4 packs, 25.6V for many 24V packs, or the correct nominal system value.
- Choose days without charging: If you plan to recharge with solar each day, be conservative about cloudy days and generator availability.
- Set planned usable capacity: 80% for LiFePO4 and 50% for AGM are conservative illustrative planning values, not universal manufacturer limits.
- Include inverter conversion losses: For AC loads, add the inverter’s losses and its idle draw; do not count these losses twice.
- Check current and BMS limits separately: A battery bank sized for energy can still fail to start a large inverter if its discharge-current rating is insufficient.
- Verify charging, protection and mounting: Check converter/solar charging profile, fuses, cable sizing, ventilation, secure mounting and low-temperature charging restrictions.
05 Calculate your battery bank
Estimate your RV battery bank
Enter measured or estimated total daily energy use. For AC loads, include inverter losses in that total. Results are approximate sizing estimates, not electrical design approval.
If this button does not update after publication, the WordPress/Elementor environment may have stripped inline scripts. Test in the published page before launch.
For battery shopping after sizing, compare 100Ah lithium batteries, 200Ah lithium batteries and lithium versus AGM. Verify those URLs are live before publication.
06 Frequently asked questions
How do I calculate RV battery amp-hours?
Add daily watt-hours, multiply by days without charging, then divide by nominal battery voltage and planned usable fraction. Adjust AC energy for inverter losses before dividing.
Why does the calculator use watt-hours?
Watt-hours represent energy consistently across 12V, 24V and 48V systems. Amp-hours without voltage do not describe a fixed energy amount.
How can I tell whether 100Ah of lithium storage covers my daily RV energy use?
It depends on actual daily watt-hours, inverter loads and days between recharges. For example, a 12.8V 100Ah pack at an 80% planning fraction represents about 1,024Wh of planned usable energy before additional system losses.
How many batteries do I need for two days off-grid?
Divide the total nominal amp-hour result by the rated amp-hours of one battery, round up, then verify the manufacturer allows the planned parallel or series arrangement.
Does solar reduce the battery bank size?
Reliable charging can reduce autonomy requirements, but solar output varies by weather, shading and season. Do not assume full rated panel output every day.
Does the calculator cover air-conditioner startup?
No. It estimates energy capacity only. Compressor starting current, inverter surge rating, BMS discharge limit and wiring must be checked separately.
07 Size for energy, then verify current
Use the calculated amp-hour requirement as a starting point, round up to a manufacturer-approved battery configuration, and check inverter surge current, BMS discharge ratings, charge sources and protective wiring separately. A precise-looking capacity estimate cannot replace actual load measurements or safe electrical design.