RV Solar Battery Sizing Guide (Amp-Hours Explained)
RV solar battery sizing determines how much battery capacity you need for reliable off-grid power. Use our RV solar calculator to size your battery bank correctly. This guide explains amp-hours, depth of discharge, and how to match your battery to your RV solar system.
Quick Answer
Most RVs need 100–400 Ah of battery capacity. Weekend campers need 100–200 Ah. Moderate off-grid use requires 200–300 Ah. Full-time boondocking demands 300–400 Ah or more. Lithium batteries provide 80% usable capacity; AGM only 50%.
Calculate Your Battery Size
Enter your appliances and daily usage to get personalized battery and solar panel recommendations. The calculator factors in depth of discharge and autonomy days automatically.
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What Is Battery Sizing?
RV solar battery sizing is the process of choosing the right capacity (in amp-hours) to store enough energy to power your RV loads overnight and during periods without sun.
Proper battery sizing balances daily energy use, battery voltage, and usable capacity to create a bank that matches your lifestyle. A battery bank that's too small leaves you powerless at night or on cloudy days. A properly sized battery gives you enough reserve energy to match your daily usage and weather variability.
What Are Amp-Hours (Ah)?
Amp-hours (Ah) measure how much energy a battery can deliver at its rated voltage over time. A 200 Ah battery can theoretically supply 20 amps for 10 hours, or 10 amps for 20 hours.
To convert amp-hours to watt-hours, multiply by voltage:
200 Ah × 12V = 2,400 Wh of stored energy
This is the total energy capacity. Usable capacity depends on battery chemistry and depth of discharge.
How to Calculate Your Daily Energy Needs
Calculate daily watt-hours by listing all appliances, multiplying watts × hours used per day, then adding them together. Convert to amp-hours by dividing by battery voltage (12V).
Example Calculation:
- Fridge: 60W × 10 hours = 600 Wh
- Lights: 20W × 5 hours = 100 Wh
- Laptop: 50W × 4 hours = 200 Wh
Total daily usage = 900 Wh
Convert to amp-hours:
900 Wh ÷ 12V = 75 Ah per day
This 75 Ah is your minimum daily draw. You'll need more capacity for autonomy and depth of discharge limits.
Battery Sizing Formula
The battery sizing formula accounts for daily usage, days of autonomy (backup), and usable capacity based on battery chemistry.
Required Ah = (Daily Wh × Days of Autonomy) ÷ (Voltage × DoD)
Example with 2 days autonomy (lithium):
- Daily usage: 900 Wh
- Days of autonomy: 2
- Voltage: 12V
- Depth of discharge: 80% (0.8)
(900 × 2) ÷ (12 × 0.8) = 1,800 ÷ 9.6 = 188 Ah
Round up to 200 Ah lithium battery bank.
Most RVers plan for 2–3 days of autonomy to cover cloudy weather or extended off-grid camping.
Battery Chemistry & Depth of Discharge (DoD)
Different battery types have different usable capacities. Lithium batteries allow 80% discharge without damage. Lead-acid and AGM should only discharge to 50% to preserve battery life.
| Battery Type | Usable DoD | Cycle Life | Cost |
|---|---|---|---|
| Lithium (LiFePO₄) | 80–100% | 2,000–5,000 cycles | $$$ |
| AGM | 50% | 500–800 cycles | $$ |
| Flooded Lead-Acid | 50% | 300–500 cycles | $ |
This means you need twice the lead-acid capacity to get the same usable energy as lithium. A 200 Ah lithium bank provides 160 Ah usable. A 200 Ah AGM bank provides only 100 Ah usable.
Practical RV Battery Capacity Ranges
Weekend campers need 100–200 Ah. Moderate off-grid users need 200–300 Ah. Full-time boondockers need 300–400 Ah or more. These ranges match most daily usage scenarios without overbuild.
| Usage Level | Battery Capacity | Solar to Match |
|---|---|---|
| Basic weekend camping | 100–200 Ah | 200–400W |
| Moderate off-grid use | 200–300 Ah | 400–800W |
| Full-time boondocking | 300–400 Ah+ | 800–1200W |
Weekend Camping
100–200 Ah
Moderate Off-Grid
200–300 Ah
Full-Time Living
300–400 Ah+
Matching Battery Bank to Solar Panels
Your solar array must produce enough energy to recharge your battery bank each day. A general rule is 200–300W of solar per 100 Ah of lithium battery. This ensures full recharge in typical sun conditions.
- Ensure panel output produces at least your daily Wh back into batteries
- A larger battery helps you ride through cloudy periods even if panels produce less
- Balance panel watts and battery capacity so neither consistently drains nor overcharges
For complete solar sizing guidance, see our RV Solar Sizing Guide.
When to Oversize Your Battery Bank
Oversizing your battery bank is beneficial if you camp in areas with frequent cloudy days, have high energy use (fridge, electronics, Starlink), or want more reserve without relying on shore power or a generator.
- Frequent cloudy weather camping
- High energy use (fridge, laptops, Starlink)
- Longer trips without shore power access
- Peace of mind and greater autonomy
A larger bank reduces stress on your system and avoids premature battery failure from frequent deep cycling.
Frequently Asked Questions
Most RVs need 100–400 Ah of battery capacity depending on usage patterns. Weekend campers often use smaller banks (100–200 Ah), while full-time off-grid RVs may require 300 Ah or more.
Amp-hours show how much energy your battery holds. To size batteries from solar, convert daily watt-hours to amp-hours by dividing by your battery voltage (typically 12V). Match solar panel output to recharge your bank daily.
Yes — planning 2–3 days of autonomy covers cloudy weather, reducing the chance of power shortfall. This is especially important for boondocking in variable weather.
Yes — a larger battery needs more solar to recharge daily, especially in limited sunlight. Balance both for efficiency. Use 200–300W of solar per 100 Ah lithium as a guideline.
Lithium batteries offer 80% usable capacity and 2,000–5,000 cycle life, but cost more upfront. AGM batteries are cheaper but only provide 50% usable capacity and 500–800 cycles. Lithium often has lower cost-per-cycle despite higher initial price.
Size Your RV Battery Bank
Use our free calculator to determine the exact battery capacity and solar panel size for your RV. Enter your appliances, get instant recommendations, and build a system that actually works off-grid.
Calculate Your Battery Size →Need help sizing solar panels too? See our RV Solar Sizing Guide for complete system planning.
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