RV BATTERY SIZING GUIDE
HOW MANY AMP-HOURS DO I NEED FOR MY RV?
Start with energy, not battery labels. Add up what you actually use in a day, convert that daily watt-hour total into amp-hours, then size the battery bank around how long you want to go between meaningful charging.
The simple answer
For a 12V LiFePO4 system, a practical first conversion is:
Daily watt-hours ÷ 12.8V = approximate amp-hours used per day
So if your RV uses about 1,280Wh per day, that is about 100Ah per day of energy at 12.8V. That does not automatically mean a 100Ah battery is the right bank. You still need reserve and you need to consider how long you want the battery bank itself to carry the loads before relying on recharge.
Worked examples
| Daily energy | Approx. 12V lithium use | Rough 1-day bank target* |
|---|---|---|
| 800Wh | 63Ah | ~100Ah |
| 1,500Wh | 117Ah | ~150Ah |
| 2,500Wh | 195Ah | ~250Ah |
| 3,500Wh | 273Ah | ~350Ah |
*Rounded planning examples using reserve. Final sizing can change with battery limits, temperature and high-current requirements.
Battery capacity is only half the question
How long should the battery cover the loads?
Choose the parked time you want the battery bank itself to cover, then evaluate solar, DC-to-DC, shore power or generator charging separately. Recharge can extend real-world runtime, but treating it separately keeps optimistic weather or driving assumptions from hiding an undersized bank.
What are the large loads?
A microwave may use little energy over a whole day but still demand high inverter current while running. Air conditioning changes the design even more. Battery capacity, inverter size, conductors and protection need to work together.
Are you measuring in watt-hours or only amps?
Watt-hours are usually the cleaner starting point because they let you combine 12V loads and 120V inverter loads in one daily energy budget. Once you know the watt-hours, converting to battery amp-hours is straightforward.
Want the math done for you?
The Heeler RV Power Calculator lets you choose common RV loads, change their wattage and daily run time, and instantly estimate Wh/day, Ah/day, solar and inverter class.
OPEN THE FREE CALCULATORCommon RV battery sizing questions
How many amp-hours does an RV use per day?
There is no single normal number. A basic RV with lights, pump, furnace fan and electronics can be relatively light. Add Starlink, a residential fridge, microwave or inverter loads and daily energy use can climb quickly. Measure the loads and run time instead of guessing from RV size.
Is a 100Ah lithium battery enough?
Sometimes. If your daily use is modest and you recharge reliably, 100Ah may work well. If your daily use is around or above the battery capacity, or you want multiple days of battery-only reserve, it will feel small quickly.
How many amp-hours do I need for two days off-grid?
Take your daily battery-side watt-hour use, multiply by two, then convert to amp-hours and leave reserve. For example, 1,500Wh/day for two days is 3,000Wh, which is about 234Ah of energy at 12.8V before reserve.
Does solar reduce the battery size I need?
For Heeler's planning method, no automatic solar credit is taken against the parked-stay battery target. Size the battery for the parked time you want it to cover, then show solar separately as energy returned per day. That makes the tradeoff visible without assuming perfect sun.
Keep planning the whole system
RV Power CalculatorCalculate daily watt-hours, amp-hours, solar and inverter starting points.RV Lithium Battery UpgradesReview battery capacity together with the converter, solar and charging system.RV DC-to-DC ChargingUse travel time to estimate battery energy returned through a controlled charging path.