RV Battery Sizing Guide

How many batteries does an RV actually need? The answer depends on what you run, how long you boondock, and whether you have solar. A weekend warrior with LED lights and a phone charger needs a very different battery bank than a full-time RVer running a residential fridge, an air conditioner, and a coffee maker.

This guide walks through the complete sizing process, from auditing your loads to choosing a chemistry to wiring your bank. No hand-waving, no vague "it depends" answers. Just the math and the trade-offs.

How an RV Power System Is Wired

RVs have two separate electrical systems that confuse many owners. The chassis battery starts the engine and powers driving systems (headlights, turn signals, engine ECU). The house battery (also called the coach battery) powers everything in the living space: lights, water pump, fridge, outlets, slides, and entertainment.

This guide is about the house battery system. You never want to drain your chassis battery running a fridge. You need that battery to start the engine and get home. A battery isolator or DC-DC charger separates the two systems, allowing the alternator to charge the house battery while driving without risking a dead engine battery at camp.

Many factory RVs ship with a single lead-acid house battery. Taking a 100Ah 12V battery as the example (an assumption for illustration, not a measured figure), 100 × 12 × 0.50 = 600Wh is usable at 50% DoD: enough for a night of light use (LED lights, water pump, phone charging) but well short of extended boondocking with a fridge, entertainment, and other comforts. Upgrading the house battery bank is one of the larger changes an RV owner can make.

Common RV Appliance Power Draws

The watts and hours in this table are example figures for illustration, not measured or maker-printed values; daily Wh is watts × hours.

For comparison, Dometic prints an energy consumption of 0.98 amp-hours per hour at 12V DC for its CFX3 35 (32°C ambient, 4°C inside), which is 0.98 × 12 = 11.76W average and 11.76 × 24 = about 282Wh a day. The 13.3W used in the table and in the examples below sits above that print: an assumption for illustration, not a measured figure.

A few things stand out. The fridge dominates daily consumption because it runs 24 hours. The air conditioner dwarfs everything else: running an RV AC on battery takes a far larger bank than the rest of the list. Short-burst appliances (coffee maker, microwave) use surprisingly little energy daily because they run for only minutes.

An inverter loses part of what passes through it. Renogy prints "over 90% efficiency" for its 2000W 12V pure sine wave inverter; this guide takes 90% as the inverter's efficiency (an assumption for illustration, not a measured figure). Through a 90% inverter, a coffee maker rated at 1,000W draws 1,000 / 0.90 = about 1,111W from the battery. That loss belongs in the sizing formula's efficiency term (0.90), and adding an allowance to the listed wattage on top of it counts the same loss twice.

How to Size Your RV Battery Bank

Use this five-step process to calculate the battery capacity your RV actually needs.

1. List your daily loads. Use the table above as a starting point. Be honest about what you actually use, not what you hope to use. If you have never boondocked before, start conservative and upgrade later. Track actual usage on your first few trips with a battery monitor. The off-grid load calculator turns that list into battery and panel recommendations; our electrical load calculator is for a house service, a dwelling's demand-factored load by the optional method that municipal worksheets print.
2. Calculate daily watt-hours. Multiply each appliance's wattage by its hours of daily use. Record each appliance's own wattage; the inverter's loss is handled once, in the sizing formula below. Sum the totals. Sarah's weekend list below (fridge, lights, water pump, phone charging, vent fan) totals 320 + 100 + 120 + 20 + 15 = 575 Wh per day. Jake's full-time list adds a residential fridge, laptop, TV and coffee maker and totals 1,680 + 240 + 400 + 240 + 150 + 100 + 45 + 30 = 2,885 Wh per day at the appliances, with no air conditioner on the list.
3. Decide your autonomy. How many days without recharging (no solar, no generator, no shore power)? This guide's example choices (assumptions for illustration, not measured figures): weekend trips, 2 days; extended boondocking with solar, 1-2 days (solar recharges daily); no solar, 3-4 days if you bring a generator for recovery charging.
4. Apply the sizing formula. Bank capacity (Ah) = (Daily Wh × Days) / (Nominal voltage × DoD × Inverter efficiency). For 1,500 Wh/day, 2 days, and a 12V LiFePO4 bank at the 12.8V nominal Victron prints for its LiFePO4 batteries and 80% DoD, with everything running through the 90% inverter above: (1,500 × 2) / (12.8 × 0.80 × 0.90) = 326 Ah, the figure the solar battery bank size calculator returns for those inputs. Use 1.00 in place of 0.90 for loads wired straight to DC. Round up to 400Ah: two 200Ah batteries or four 100Ah batteries in parallel (2 × 200 = 4 × 100 = 400Ah, against the 326 Ah).
5. Check physical fit. Measure your RV's battery compartment before buying. LiFePO4 batteries are smaller than lead-acid for the same capacity, but compartment dimensions still limit what fits. Group 24, 27 and 31 are battery case sizes found in RVs. Some 100Ah LiFePO4 batteries come in Group 24 or Group 31 cases for drop-in replacement.

Skip the manual math and use the RV battery runtime calculator for instant results based on your specific loads.

Battery Chemistry Comparison for RVs

Four battery types are commonly used in RVs. Each has trade-offs in cost, weight, lifespan, and maintenance.

Flooded lead-acid (FLA)

Cheapest upfront. Requires regular maintenance: checking water levels monthly and equalizing quarterly. Produces hydrogen gas during charging, requiring ventilation. Heavy for its capacity. Trojan recommends discharging 20 to 50% of rated capacity on its flooded deep-cycle batteries, and prints 80% as what the battery is capable of rather than what it advises. Best for: budget builds with easy compartment access for maintenance. Not suitable for sealed or interior-mounted battery boxes.

AGM (Absorbed Glass Mat)

Sealed, maintenance-free. No water to add, no hydrogen venting. Can be mounted in any orientation. Same 50% DoD as flooded lead-acid and a similar weight, at a higher price; Victron prints 600 cycles at 50% depth for its 12V Deep Cycle AGM. To see what a given AGM pair holds against your own evening load, run it through the AGM battery runtime calculator. Best for: upgraders who want drop-in simplicity without the maintenance of flooded batteries or the cost of lithium.

LiFePO4 (Lithium Iron Phosphate)

A deeper usable DoD than lead-acid (this guide's examples use 80%), a cycle life of 2,500 at 80% DoD (Victron) and 3,000-5,000 at 100% (Battle Born), and Victron prints a weight saving of up to 70% against lead-acid. No maintenance, no venting, consistent voltage under load. It costs more than lead-acid up front and lasts many more cycles. Requires a compatible charger/converter and charge controller. Best for: anyone who boondocks regularly, values weight savings, or plans to keep the RV for years. Read the full comparison in our LiFePO4 vs lead-acid guide.

6V golf cart batteries (flooded lead-acid)

A traditional RV upgrader's choice: wire two 6V batteries in series for 12V. Trojan's T-105 is the classic. Thicker plates than standard 12V batteries give them long cycle lives: U.S. Battery prints 1,150 cycles at 50% DoD for its US 2200, a 6V golf cart battery of the same class. Heavy and need regular watering, but deliver excellent value per cycle. Best for: budget-conscious boondockers willing to do maintenance and who have the space for larger batteries.

Weekend Boondocking vs Full-Time: Two Sizing Examples

Weekend boondocker: Sarah's truck camper

Sarah takes her truck camper out 30 weekends per year. She arrives at 6 pm Friday and leaves at 2 pm Sunday: 6 + 24 + 14 = 44 hours off-grid. Her weekends, times and loads are this example's figures, assumptions for illustration, not measured:

• 12V compressor fridge: 13.3W avg × 24h = about 320 Wh/day
• LED lights: 25W × 4h = 100 Wh/day
• Vent fan: 20W × 6h = 120 Wh/day
• Phone charging: 10W × 2h = 20 Wh/day
• Water pump: 60W × 0.25h = 15 Wh/day

Total: 575 Wh/day, all of it DC loads (inverter efficiency 1.00). For 2 days of autonomy with a 12V LiFePO4 bank at 80% DoD, the solar battery bank size calculator returns 112 Ah:

(575 × 2) / (12.8 × 0.80 × 1.00) = 112 Ah

Sarah installs a single 300Ah 12V LiFePO4 battery, about 2.7 times her 112 Ah two-day need (300 / 112 = 2.7). It fits in her truck camper's battery box. The same two days in a 12V lead-acid bank at 50% DoD is (575 × 2) / (12 × 0.50 × 1.00) = 192 Ah in the same calculator, so two 100Ah batteries in parallel (2 × 100 = 200 Ah, against the 192 Ah), with the extra weight lead-acid carries. Her one 200W roof-mounted panel returns 807 Wh a day in the solar panel output calculator at the 5.18 peak sun hours PVWatts prints for Kansas City and 14% losses: 807 - 575 = 232 Wh a day more than she uses, which stretches her autonomy past 2 days while the sun is out.

Prices move, so check current ones for the battery, the solar panel and the MPPT controller before you buy. At 30 cycles a year, the 3,000 cycles at the low end of Battle Born's print above would take 3,000 / 30 = 100 years to use up. If you want to verify these numbers with your own loads, our battery runtime calculation guide walks through every variable in the formula.

Full-time RVer: Jake's fifth wheel

Jake lives in his fifth wheel full-time, boondocking 3-4 nights per week and spending the rest on shore power. His nights off-grid and his loads, which are higher, are this example's figures, assumptions for illustration, not measured:

• Residential fridge (AC via inverter): 70W avg × 24h = 1,680 Wh/day
• LED lights: 40W × 6h = 240 Wh/day
• Vent fans (2): 50W × 8h = 400 Wh/day
• Laptop: 60W × 4h = 240 Wh/day
• TV: 50W × 3h = 150 Wh/day
• Coffee maker: 1,000W × 0.1h = 100 Wh/day
• Phone/tablet: 15W × 3h = 45 Wh/day
• Water pump: 60W × 0.5h = 30 Wh/day

Total: 2,885 Wh/day at the appliances: 2,170 Wh of AC loads (residential fridge, laptop, TV, coffee maker) and 715 Wh of DC loads (lights, vent fans, phone/tablet, water pump). For 2 days of autonomy (covering his longest boondocking stretches):

AC loads 2,170 Wh/day through the 90% inverter = 2,170 / 0.90 = 2,411 Wh; DC loads 715 Wh/day; 2,411 + 715 = 3,126 Wh drawn from the battery each day. With the inverter's loss already counted, the solar battery bank size calculator at 3,126 Wh a day, 2 days, a 12V LiFePO4 bank, 80% DoD and 100% inverter efficiency returns 611 Ah: (3,126 × 2) / (12.8 × 0.80 × 1.00) = 611 Ah

Jake installs four 200Ah 12V LiFePO4 batteries in parallel (4 × 200 = 800Ah, against the 611 Ah), a pure sine wave inverter for his AC loads, and three 200W panels (600W) of rooftop solar with an MPPT controller. Victron prints 20 kg for its 12,8V 200Ah LiFePO4 battery, so four of that model weigh 4 × 20 = 80 kg.

At the 5.18 peak sun hours PVWatts prints for Kansas City and 14% losses, the solar panel output calculator returns 2,422 Wh a day for his three 200W panels. The panels supply 2,422 / 3,126 = 77.5% of the 3,126 Wh he draws; the other 3,126 - 2,422 = 704 Wh a day (704 / 3,126 = 22.5%) is the shortfall. On cloudy days, he tops off with a portable generator. He chose not to run AC on battery: at the 7,200-10,800 Wh per day in the table above, that would take a far larger bank than his 800Ah and a far larger solar array. Instead, he uses shore power or a propane generator for AC when needed.

The camper battery calculator counts batteries for a camper from a daily usage, and the solar panel and battery sizing calculator sizes a panel array and a battery bank from a daily usage.

Charging Your RV Battery Bank

A battery bank is only as useful as your ability to recharge it. RVs have three common charging sources:

Shore power. The RV's built-in converter/charger tops off the battery bank whenever you plug in. Make sure your converter supports your battery chemistry: a converter set for lead-acid charging profiles can undercharge LiFePO4 without a firmware update or replacement. A quality 3-stage converter from Progressive Dynamics or WFCO with a LiFePO4 profile works well.

Solar panels. Roof-mounted solar with an MPPT charge controller provides silent, maintenance-free daily recharging. Sarah's example above runs one 200W panel and Jake's runs three; the solar panel output calculator turns panel wattage, number of panels, peak sun hours and system losses into watt-hours a day to set against your own daily use. Solar output varies dramatically by season and location: see our solar panel output guide for realistic expectations.

Alternator charging (DC-DC). A DC-DC charger (like a Victron Orion or Redarc BCDC) takes power from the engine alternator while driving and delivers it to the house battery at the correct voltage and current. A DC-DC charger delivering its full rating of 30 to 40A (example ratings, assumptions for illustration, not measured figures) adds 30A × 1h = 30Ah to 40A × 1h = 40Ah per hour of driving, enough to recharge part of the bank during travel days. For a 100Ah house battery, how long a 100Ah battery takes to charge puts that against solar and shore power. This is especially valuable for truck camper and van life setups that drive frequently between camps.

A well-designed RV power system uses all three sources: solar for daily passive charging, the alternator for recharging during travel, and shore power for full recovery when available. The battery bank acts as the buffer that absorbs and releases energy as needed. With the bank sized, our guides on what size inverter you need and what size battery charger you need cover the inverter that draws from it and the charger that refills it.