How Many Amp-Hours Do I Need for My RV?
Convert an RV daily energy budget into battery amp-hours without mixing up voltage, usable capacity and inverter losses.
Amp-hours are meaningful only at a stated voltage. Start with watt-hours because RV loads may span 12V DC and 120V AC.
RV battery sizing should start in watt-hours, then convert to amp-hours at the battery-bank voltage. Asking for “how many amp-hours” without specifying voltage and daily energy use can produce a misleading answer.
What matters
- Add daily energy in Wh across DC and AC loads.
- Account for inverter losses on AC appliances.
- Convert final Wh to Ah at the battery-bank voltage.
- Preserve reserve rather than planning around 100% depletion.
Decision factors that change the answer
Build a daily Wh budget
Multiply each load by hours of use, then add the results. This works across 12V and AC appliances.
Convert to Ah
Ah = Wh ÷ nominal battery voltage. A 1,280Wh target is about 100Ah at 12.8V but only about 50Ah at 25.6V.
Reserve
Do not size the bank to reach empty every day. Add reserve for weather, extra device use and battery aging.
Recharge rate
Solar and alternator charging must replace the daily energy consumed or the bank declines over successive days.
How to size it
- List each load and daily hours.
- Calculate Wh per load and total them.
- Apply reserve/efficiency factors.
- Divide target Wh by nominal battery voltage to estimate Ah.
A 1,280Wh target corresponds to about 100Ah at 12.8V nominal, before reserve and conversion assumptions.
Worked example
If an RV uses 1.5kWh/day, a one-day nominal target at 12.8V is about 117Ah before reserve and losses. At 25.6V, the same energy is about 59Ah. This is why Ah numbers cannot be compared across voltages without converting back to Wh.
Common buying mistakes
- Adding amp-hours from devices at different voltages.
- Sizing from one unusually light camping day.
- Ignoring high-energy loads like air conditioning or electric cooking.
Build the RV budget in watt-hours first; convert to amp-hours only after the system voltage is fixed.
Check the underlying numbers
Use these site resources to replace generic assumptions with your own load or the source-linked data behind this guide.
Use the numbers before choosing a model
Start with your load list. The battery needs enough watt-hours for the desired runtime and enough continuous/surge watts to operate the appliances at the same time. Then check whether your recharge method can replace the energy you expect to consume.
For outage planning, we recommend keeping reserve capacity instead of designing a system that reaches 0% at the end of the forecasted outage.
Next step
Estimate battery runtime → or Build a critical-load energy budget →.