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RV Battery Bank Calculator: Amp-Hours, AGM vs Lithium, and Charging Time

Built and reviewed by (MBA Finance) · Updated October 2026

Build your load from real appliances, not a guess. This calculator sizes your battery bank from the ground up, then shows you AGM vs lithium side by side with actual Ah, weight, upfront cost, lifetime cost, and how long your solar or shore power takes to recharge it.

🔋 Build Your Daily Load
💡 Appliance Load Builder (edit watts and hours)
Appliance Watts Hrs/Day Wh/Day
Total Daily Energy – Wh
DC loads run directly. AC loads (laptop, TV, kitchen) go through your inverter: 10% efficiency loss added automatically. Adjust any wattage or hours above.
📊 Or Enter Daily Wh Directly
Wh/day
The appliance table above auto-fills this. You can override it with a known value from a battery monitor or energy meter.
⚙️ Bank Settings
days
Days without solar/shore power. Weekend = 2. Full-timer boondocking = 3-4.
🔌 Charging Sources (optional)
W
hrs
US average: AZ/NV = 6-7, SE/Midwest = 4-5, PNW = 3-4
A
Typical: 45A built-in converter, or 60-100A external charger. Calculates shore power recharge time.
📊 Battery Bank Analysis
🔋
Fill in your appliance load and click Calculate. The analysis shows required Ah, AGM vs lithium side-by-side with weight and cost, number of batteries, and recharge time from solar or shore power.

Why Your RV Battery Bank Needs to Be Bigger Than the Math Suggests

The most important concept in RV battery sizing is the difference between nameplate capacity and usable capacity. Every battery has a number printed on the label: 100Ah, 200Ah, whatever, and that number is the total stored energy. What it does not tell you is how much of that energy you can safely withdraw before the battery is damaged or its cycle life drops dramatically.

For AGM and flooded lead-acid batteries, the safe depth of discharge is 50 percent. A 100Ah AGM battery delivers 50 usable amp-hours before you should stop and recharge. If you draw it deeper than that regularly, the sulfation process accelerates and the battery loses capacity permanently over a period of months. This is why experienced RV technicians who see batteries with 30 to 40 percent of their original capacity after two seasons inevitably find that the owner was running the bank to near-empty before recharging. The 50 percent limit is not a manufacturer suggestion. It is the boundary between normal aging and accelerated destruction.

Why LiFePO4 Changes the Calculation Completely

Lithium iron phosphate batteries (LiFePO4, or simply LFP) operate with an 80 to 90 percent usable depth of discharge. That same 100Ah battery delivers 80 to 90 usable amp-hours rather than 50. This single difference means that a 100Ah lithium battery replaces 160 to 180Ah of AGM capacity. The math sounds counterintuitive until you work through it: to get 200Ah of usable power from AGM, you need a 400Ah nameplate bank. To get 200Ah of usable power from lithium, you need a 250Ah nameplate bank. You need less than two-thirds the nameplate capacity to deliver the same usable energy.

The weight advantage compounds this. AGM batteries weigh approximately 13 lbs per 100Ah. Lithium batteries weigh approximately 6.5 lbs per 100Ah. A 400Ah AGM bank weighs roughly 520 lbs. A 250Ah lithium bank delivering the same usable energy weighs roughly 163 lbs. That is a 357-lb weight savings for identical usable capacity. In a travel trailer or Class B van where every pound affects fuel economy and handling, this difference is significant.

The Autonomy Multiplier: Why Two Days Is the Minimum

Days of autonomy is the multiplier that most battery bank calculations underestimate. One day of autonomy sounds logical, you use energy all day and solar recharges it the next day. But solar output is inconsistent. A partly cloudy day in Oregon might produce 30 percent of rated output. A rainy day in the Florida Keys might produce 10 percent. Two consecutive days of poor solar production, which happens constantly in the Pacific Northwest and intermittently everywhere, will drain a one-day autonomy bank entirely. Most experienced boondockers target two to three days of autonomy as a practical minimum, with four days reserved for extended remote camping in northern climates where winter sun is limited.

How the Amp-Hour Formula Works: Load, Autonomy, Depth of Discharge

The battery bank sizing formula has three inputs: daily energy use in watt-hours, days of autonomy, and the usable depth of discharge for your battery chemistry. Working through each input explains where the final Ah number comes from and why changing any one input changes the result significantly.

Daily Energy Use: Why the Appliance Builder Matters

Entering a single “daily Wh” number without knowing where it comes from is the leading cause of undersized battery banks. People guess their consumption optimistically, leave out appliances they use occasionally, and forget the inverter efficiency loss. This calculator’s appliance builder requires you to assign wattage and hours to each device, which forces a realistic accounting of the actual load. The default values are based on measured power consumption of common RV appliances, not marketing specifications. A 12V compressor fridge, for example, is listed at 55W average draw, not the 200W peak compressor current that appears on some product pages.

AC appliances (anything that runs through your inverter, like a laptop, TV, or coffee maker) carry a 10 percent efficiency penalty in this calculator. A 900W coffee maker running for 6 minutes actually draws 900W from the inverter plus 10 percent overhead from the inverter itself, for an effective draw of 990Wh from the battery for that 6-minute run. Small numbers per appliance add up to hundreds of watt-hours per day when you look at the full picture.

System Voltage and Its Effect on Wire Size

Most RVs use a 12V battery bank. As total power needs grow beyond roughly 3,000 to 5,000 watt-hours per day, a 24V system becomes more practical because the same wattage at double the voltage requires half the current, which means you can use smaller wire gauges and have lower resistive losses in long wire runs. Very large systems in converted buses or off-grid trailers sometimes use 48V. This calculator supports all three common voltages and adjusts the Ah requirement accordingly. The same 3,000Wh daily load requires 250Ah at 12V, 125Ah at 24V, or 62.5Ah at 48V, the energy is identical but the configuration of the bank changes.

Three Real US Boondocking Scenarios with Complete Battery Bank Numbers

Scenario 1 in Colorado: Weekend Warriors in a 27-ft Travel Trailer

Mike and Susan take their 2020 Keystone Cougar to Rocky Mountain National Park for long weekends, typically Friday afternoon through Sunday. They run a 12V compressor fridge, LED lights, a roof vent fan overnight, phone charging, and laptop use. No AC, no microwave. They want to operate without hookups for 2 nights.

ApplianceWattsHoursWh/Day
12V Compressor Fridge55W avg24 hrs1,320 Wh
LED Lights25W4 hrs100 Wh
Roof Vent Fan35W8 hrs280 Wh
Phones / Tablets30W3 hrs90 Wh
Laptop (via inverter)65W3 hrs216 Wh (w/ inverter loss)
Total2,006 Wh/day
2 days autonomy / 80% DoD (lithium)251 Ah LiFePO4
2 days autonomy / 50% DoD (AGM)402 Ah AGM

Mike and Susan’s weekend load is modest. The lithium bank at 300Ah nameplate (2x 150Ah or 3x 100Ah batteries) covers their 2-day need with a safety margin. A 400Ah AGM bank covers the same need but weighs roughly 520 lbs vs 195 lbs for 300Ah of lithium. At 9,000 to 10,000-ft elevation in Colorado where engine power is reduced, the 325-lb weight savings is meaningful for fuel economy and braking on mountain grades.

Scenario 2 in Quartzsite, AZ: Full-Timers with Heavy AC Use

Debra and Jim full-time in a 38-ft fifth wheel at the famous Quartzsite, AZ winter gathering. They have two slide-outs, run a 15,000 BTU AC for 3 hours in the afternoon, a large compressor fridge, two workstations, a Starlink dish, and run the microwave daily. They want 3 days of autonomy with 800W of solar.

Major LoadsWattsHoursWh/Day
15,000 BTU AC (via inverter)1,560W3 hrs5,200 Wh
12V Fridge70W avg24 hrs1,680 Wh
Two Laptops + monitors (via inv.)180W6 hrs1,200 Wh
Starlink dish (DC)50W10 hrs500 Wh
Microwave, coffee, misc. (inv.)1,200W0.35 hrs467 Wh
Lights, fans, water pump80W avg8 hrs640 Wh
Total~9,687 Wh/day
3 days / 80% DoD lithium + 800W solar (5 hrs)3,632 Ah needed / solar provides 3,200 Wh/day
Practical: 600Ah LiFePO4 + generator for AC hoursPure battery can’t cover 3 days with AC – generator needed

Debra and Jim’s setup highlights the practical limit of battery-only power for RVs running AC regularly. Three days of 9,687 Wh/day would require a 36,380Wh bank (3,032Ah at 12V), which is both impractical in size and cost. The realistic configuration is a 600 to 800Ah lithium bank plus solar to cover all loads except the AC unit, and a generator for the 3-hour AC window. The battery bank then handles all overnight and most daytime loads while the generator charges the bank during AC operation.

Scenario 3 in Pacific Northwest: Van Lifer with 4-Day Autonomy

Alex lives in a converted Sprinter van in the Cascades. The van has a 200W solar array but the Pacific Northwest has consistently cloudy winters (average 3 peak sun hours in winter vs 5.5 in summer). Alex runs a small fridge, LED lights, laptop for remote work, and phone charging. No AC. Alex wants 4 days of autonomy to cover multi-day cloudy stretches.

ApplianceWattsHoursWh/Day
12V Compressor Fridge (small)40W avg24 hrs960 Wh
LED Lights20W4 hrs80 Wh
Laptop (via 300W inverter)65W6 hrs433 Wh
Phone charging + USB gear30W3 hrs90 Wh
Roof vent fan20W6 hrs120 Wh
Total1,683 Wh/day
4 days autonomy / 80% DoD (lithium)281 Ah LiFePO4, use 300Ah bank
200W solar @ 3 hrs/day (winter)480 Wh/day generated vs 1,683 Wh used, deficit of 1,203 Wh/day

Alex’s calculation reveals the inconvenient truth of Pacific Northwest van life in winter: 200W of solar at 3 peak sun hours generates only 480Wh per day against a 1,683Wh daily need. Four days of autonomy covers the deficit for four days, but by day 5, Alex needs to drive (alternator charging), find a shore power connection, or add more solar panels. The practical solution for winter van life in the PNW is a 300Ah lithium bank plus a 600W to 800W solar array to minimize charging gaps, accepting that some generator or alternator charging will be needed during extended cloudy periods.

Three Expert Tips for Getting More from Your RV Battery Bank

Tip 1: Never Buy Your Batteries Based on Name Brand Alone: Check the BMS

The Battery Management System (BMS) is the circuit board inside a lithium battery that monitors cell voltage, temperature, and current to protect the cells from overcharge, over-discharge, and thermal events. A quality BMS is the difference between a lithium battery that lasts 10 years and one that fails catastrophically within two seasons. When evaluating lithium batteries for RV use, verify: that the BMS has low-temperature charge cutoff protection (protects against charging below freezing), that the continuous discharge rating matches your maximum inverter output, that the BMS has cell balancing capability, and that the manufacturer publishes the BMS specifications rather than hiding them.

Domestic brands like Battle Born, Lithionics, and Epoch Batteries publish detailed BMS specifications. Many imported batteries available on Amazon and through discount channels conceal BMS specifications because they use lower-grade BMS hardware. A $100 difference in battery price can easily cost you $1,000 in premature replacement if the BMS fails to protect cells during a charging event.

Tip 2: Match Your Charger to Your Battery Chemistry: Mismatched Chargers Destroy Batteries

Most RVs come with a converter/charger that was designed for lead-acid batteries. If you swap to lithium without upgrading the charger, you will likely overcharge your lithium bank. AGM charging profiles typically charge to 14.4 to 14.8V in absorption and float at 13.2 to 13.6V. LiFePO4 batteries charge to 14.4 to 14.6V but must not be held in a float stage because continuous float charging at even a low voltage causes lithium to plate and damages cells. A quality multi-stage charger designed for LiFePO4 (such as the Victron Blue Smart or the Progressive Dynamics PD9260LV) will apply a bulk charge, absorb to full, and then completely shut off rather than maintaining a float charge. This is a non-negotiable upgrade when switching to lithium.

Tip 3: Monitor Your Battery Bank: A Shunt-Based Monitor Is Mandatory for Accuracy

The factory battery gauge on most RVs measures voltage, which is a poor proxy for state of charge in any battery chemistry. A resting 12V AGM battery at 12.5V is at roughly 75 percent charge. A resting LiFePO4 battery at 12.5V is at roughly 30 percent charge. Reading voltage without understanding chemistry-specific state-of-charge curves leads towers to think they have more power than they do. A shunt-based battery monitor (Victron SmartShunt, Renogy 500A shunt monitor, or similar) measures actual amp-hours in and out of the battery, giving a precise state-of-charge reading regardless of battery chemistry. For a serious boondocking setup, a $50 to $150 battery monitor is as important as any component in the electrical system. Without accurate SOC data, you cannot manage your power budget effectively.

16 RV Battery Bank Questions Answered for US Boondockers

Full-time RV living without air conditioning typically requires 2,000 to 4,000 watt-hours per day (Wh/day) depending on occupants, appliances, and work-from-home electronics. With air conditioning, daily loads jump to 6,000 to 12,000 Wh/day or more. For 2 days of autonomy at 3,000 Wh/day on a 12V lithium system (80% DoD), you need approximately 3,000 Wh x 2 days divided by (12V x 0.80) = 625Ah of nameplate lithium capacity. Most serious full-timers run 400 to 800Ah of lithium in a 12V system, paired with 600 to 1,600 watts of solar, accepting that air conditioning requires generator or shore power.
Both AGM and flooded lead-acid are lead-acid chemistry with 50 percent usable depth of discharge. AGM (Absorbed Glass Mat) is sealed, maintenance-free, and can be mounted in any orientation. Flooded lead-acid requires monthly watering (adding distilled water to replace water lost through gassing), must be mounted upright with ventilation for hydrogen gas, and is significantly cheaper per amp-hour. AGM handles partial state-of-charge conditions better than flooded and charges faster. Both are significantly heavier and shorter-lived than lithium for the same usable energy. For RV use where maintenance access is difficult and batteries may sit partially discharged for weeks between camping trips, AGM is the practical lead-acid choice over flooded.
No. Mixing battery chemistries in the same bank is strongly inadvisable. LiFePO4 and AGM batteries have different voltage profiles, different charge/discharge curves, and different optimal charging voltages. When connected in parallel, the chemistry with the higher voltage at any given state of charge will drive current into the other, potentially overcharging or undercharging one or both chemistries. The BMS in a lithium battery is also designed to protect lithium cells, not to manage the very different behavior of lead-acid cells connected in parallel. If you are upgrading from AGM to lithium, replace all batteries in the bank at the same time with the same chemistry, and update your charger profile accordingly.
A 200Ah lithium battery at 12V holds 2,400Wh of total energy and 1,920Wh of usable energy at 80% DoD. To recharge 1,920Wh from empty with a 400W solar array at 5 peak sun hours per day: 400W x 5hrs x 0.80 efficiency = 1,600Wh per day. So you need about 1.2 days of good solar to fully recharge. With a 600W array at the same conditions: 600 x 5 x 0.80 = 2,400Wh per day, so about 0.8 days. These are theoretical numbers assuming the battery accepts full current throughout, lithium batteries charge at near-constant current until approximately 95% full, then taper, so real-world times are close to these estimates unlike lead-acid which tapers much earlier.
The most widely recommended LiFePO4 battery brands for US RVers in 2025 and 2026 include Battle Born (made in Reno NV, premium pricing, excellent BMS and warranty support), Lithionics (higher voltage and custom configurations), Epoch Batteries (competitive pricing with solid BMS specs), Renogy (broad availability and good value at mid-tier pricing), SOK Battery (popular in the van life community for price-to-performance), and LiTime (formerly Ampere Time, budget-tier but functional BMS). For serious full-time boondocking where battery failure means no power in a remote location, Battle Born and Lithionics command premium prices that are justified by their US-based customer support and warranty service. For occasional boondockers comfortable with Amazon returns, Renogy and Epoch provide good value at lower price points.
State of charge (SOC) is the percentage of a battery’s total capacity that is currently stored, similar to a fuel gauge. A 100Ah battery at 50% SOC has 50Ah remaining. Managing SOC is critical for two reasons: discharging below the recommended minimum SOC damages the battery (50% for lead-acid, 20% for lithium), and overcharging above 100% SOC also damages cells. A shunt-based battery monitor tracks cumulative amp-hours in and out of the battery to calculate actual SOC with high accuracy. Voltage-based SOC readings on standard RV battery monitors are unreliable because battery voltage changes with load, temperature, and the specific chemistry’s discharge curve, making voltage-to-SOC conversion inaccurate except at rest.
For a 12V 200Ah bank using 12V 100Ah batteries, you need 2 batteries wired in parallel (positive to positive, negative to negative). This doubles the amp-hour capacity while keeping the voltage at 12V. If you are building a 200Ah bank using 6V batteries (such as golf cart batteries), you need 4 batteries: 2 pairs wired in series to make 12V, then the two 12V pairs wired in parallel. Always use identical batteries (same brand, model, and age) in a parallel bank, and use equal-length cables from each battery to the bus bar or terminal to ensure balanced current distribution. Do not mix old and new batteries in a parallel bank.
For most RVers who camp regularly with some boondocking, yes. The break-even analysis favors lithium when you factor in lifetime cost. A 200Ah AGM bank costing roughly $280 needs to be replaced every 2 to 3 years with regular use, for a 10-year total of $840 to $1,400. A 200Ah lithium bank costing roughly $500 lasts 10 to 15 years. Add the weight savings (260 lbs AGM vs 130 lbs lithium for the same nameplate), the doubled usable capacity, faster charging, and better compatibility with solar systems, and lithium is the better long-term investment for anyone who camps more than 20 nights per year. For occasional campers who use hookups most of the time and rarely boondock, AGM remains a reasonable and more affordable choice.
Yes, for short durations. A 1,500W inverter at 12V draws approximately 125 amps from the battery bank. A 100Ah lithium battery can typically deliver 100 amps continuous and 200 amps for 5 to 10 seconds for startup surges, depending on the BMS specs. Running 125 amps from a 100Ah battery means the bank would be discharged in less than 45 minutes (ignoring inverter efficiency). For extended inverter use, size the battery bank so that the continuous inverter draw represents no more than 0.5C (half the capacity in amp-hours). A 1,500W inverter drawing 125A should ideally run from a 250Ah bank or larger. Also verify that your wire gauge from battery to inverter is adequate for 125A continuous, this typically requires 2/0 AWG or 4/0 AWG cable depending on run length.
Size your inverter to handle the maximum simultaneous AC load plus a 20 to 25 percent safety margin. If your heaviest simultaneous AC loads are a laptop (65W), TV (80W), and charging two phones (30W), that is 175W running, a 300W inverter handles this easily. If you add a coffee maker (900W) that runs by itself, you need at least a 1,200W inverter for the coffee maker alone. For RVs that run air conditioning through the inverter, the AC draws 1,365 to 1,560W plus startup surge of 4,000 to 5,000W, you need a 2,000 to 3,000W pure sine wave inverter with high surge capacity, paired with a soft-start kit to manage the startup surge. Never use a modified sine wave inverter with AC motors (compressors, fans) or sensitive electronics.
The four most common causes of premature RV battery failure are: (1) Over-discharge, regularly drawing lead-acid below 50% SOC or lithium below 20% SOC accelerates cell degradation; (2) Chronic undercharging, leaving batteries in a partial state of charge for weeks causes sulfation in lead-acid and can strain BMS electronics in lithium; (3) Overcharging, a charger with an incompatible charge profile applies too much voltage for too long, cooking cells over time; and (4) High-current abuse, drawing more than the battery’s rated maximum continuous current stresses internal cell connections. For lead-acid, the combination of deep discharge and slow, incomplete recharging is the single most common battery killer in RV applications where owners run the bank flat camping and then spend weeks at home where the battery sits uncharged.
Alternator charging replenishes your house battery bank while the tow vehicle or motorhome engine is running. Most RVs have a battery-to-battery (B2B) charger or a battery isolator that routes alternator output to the house bank. A typical B2B charger delivers 20 to 60 amps of charge current, which for a 200Ah lithium bank means 3 to 10 hours of driving to fully recharge from empty. Alternator charging is a viable supplement to solar for boondockers who drive frequently, a 3-hour drive at 40 amps adds 120Ah to the house bank. However, relying solely on alternator charging requires understanding both the charge current available and the total energy needed, and avoiding the mistake of thinking short 30-minute drive segments meaningfully recharge a large bank.
Peak sun hours (PSH) is the number of hours per day when solar irradiance averages at least 1,000 watts per square meter, the standard solar panel test condition. The NREL (National Renewable Energy Laboratory) publishes detailed peak sun hour data for every US location at pvwatts.nrel.gov, free to access. US regional averages: Arizona and Nevada desert: 6.5 to 7.0 PSH in summer; Texas Gulf Coast: 5.0 to 5.5 PSH; Southeast: 4.5 to 5.5 PSH; Midwest: 4.0 to 5.0 PSH; Pacific Northwest: 4.5 to 5.5 PSH in summer, 2.5 to 3.5 PSH in winter; Northeast: 3.5 to 4.5 PSH. Always use winter PSH values if you camp year-round, as they are significantly lower than summer values and determine your worst-case charging scenario.
12V is the standard for most RVs and is compatible with the widest range of off-the-shelf components, appliances, and solar charge controllers. 24V becomes advantageous when daily energy needs exceed roughly 4,000 to 5,000Wh per day, because the same wattage at 24V requires half the current, allowing significantly smaller wire gauges and reducing I-squared-R resistive losses in long cable runs. A 3,000W inverter at 12V draws 250 amps, requiring very thick cables. The same 3,000W at 24V draws 125 amps, allowing more practical wire sizing. Motorhome and Class A converters are commonly 12V. Large off-grid trailers and bus conversions often use 24V or 48V. Unless you have a specific reason to step up (typically total system size or inverter size above 3,000W), 12V keeps your system simpler and parts more accessible.
Every battery bank must have an appropriately sized fuse or circuit breaker at the positive terminal, as close to the battery as possible. The fuse protects the wiring, not the battery, if a wire shorts, the fuse blows before the wire becomes a fire hazard. Size the fuse for the wire gauge, not the load: 4 AWG wire handles approximately 100A and should be protected by a 100A fuse; 2/0 AWG handles approximately 265A and uses a 250 to 300A fuse; 4/0 AWG handles approximately 360A. ABYC (American Boat and Yacht Council) and NFPA 303 standards provide detailed wire sizing and fuse tables that apply equally well to RV electrical systems. For lithium battery banks, a Class T fuse is strongly recommended over automotive blade fuses because Class T fuses blow much faster under high fault currents, providing better protection for lithium cell short circuits.
The clearest sign is a battery monitor showing you regularly reach 20 to 30% SOC before solar or shore power restores the bank. If you are waking up to a battery monitor reading below 30% SOC on most boondocking mornings, you either need more battery capacity or more solar input. Track your actual daily consumption with a battery monitor for one week of typical camping to get an accurate baseline, then run the numbers through this calculator to determine whether additional capacity or additional solar (or both) is the right investment. Adding solar is often more cost-effective than adding batteries if your bank is adequately sized but not being fully recharged each day, solar keeps the bank topped up; batteries provide the overnight reservoir.

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Legal Disclaimer and Editorial Transparency

Battery sizing estimates in this calculator are based on published specifications for typical battery chemistries and common appliance power consumption data. Actual performance varies by battery brand, temperature, age, and specific BMS implementation. Cost estimates reflect approximate 2025-2026 US retail pricing and will change over time. Cycle life estimates are based on manufacturers’ published data at stated depth of discharge conditions; actual cycle life varies with charging practices, temperature, and battery quality.

This calculator is for planning and comparison purposes only. Electrical system design for RVs involves safety considerations including proper fusing, wire sizing, and code compliance that should be reviewed by a qualified RV electrician or RVIA-certified technician. USCalculators.com is not responsible for equipment damage, fire, or personal injury resulting from battery installations based on this calculator. Editorial transparency: No battery manufacturer, solar company, or electrical equipment brand paid to influence the content or recommendations on this page.

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