Skip to content
Free tool · RV power

How long will your RV battery last?

Enter the battery bank you already have, tick the 12V loads you run, and this tool returns how long it lasts: days at your daily draw, how long it runs the fridge alone, and hours at a heavy load, with the lead-acid Peukert penalty most calculators ignore. A planning estimate, not a substitute for a battery monitor on your actual bank.

Read first: this is a free planning estimate using accepted battery math, not a measurement of your actual bank. Real runtime depends on your battery's age and health, the temperature, the true draw of your gear, and inverter losses. Use it to plan and shop, and for the real number on your rig, fit a battery monitor (shunt). Never charge a LiFePO4 battery below freezing without an internal heater.

Your battery bank

Your daily loads

Tick what you run and set the hours per day. Amps are typical duty-averaged 12V figures; check your own gear where you can.

Use Load Amps Hrs/day
duty-averaged; about 30 to 50 Ah/day for a 12V box 4
about 4.5 A high, 0.2 A low 2.5
2
on-demand, brief 5
3.5
always-on parasitic 0.1
cold nights only 6
8 to 10 A on glow startup, then ~1 A 1
the big new draw for remote workers 4.5
3
1.5
2

A planning estimate using accepted battery math. For the real number on your rig, a battery monitor (shunt) measures actual capacity and draw.

How the runtime math works

The calculator above is just this method, applied to the bank and loads you pick. You can run it by hand.

Step 1: Start with usable capacity, not the label

A battery's rated amp-hours are not all yours to use. Lead-acid (flooded, AGM, gel) should only be drawn to about 50% before you shorten its life; LiFePO4 lithium is commonly planned to about 80%. So a 100 amp-hour lead-acid battery gives roughly 50 usable amp-hours, while a 100 amp-hour lithium gives about 80. Usable capacity is bank amp-hours times that usable share, and it is the number every runtime estimate has to start from.

Step 2: Add up your daily draw, then divide

List the 12V loads you run and the hours per day for each, total it to amp-hours per day, and divide your usable capacity by that daily draw to get days of runtime before you need to recharge. The 12V compressor fridge is almost always the biggest single load because it runs around the clock, even though it only sips while the compressor is cycling. The math is simple; the honesty is in using your real loads and a realistic usable share.

Step 3: Lead-acid gives less under a heavy load (Peukert)

A battery's amp-hour rating is measured at a slow 20-hour discharge. Pull current faster and lead-acid delivers measurably less than its rating: roughly 25% less at the 5-hour rate and up to 40% less at a hard inverter-level draw. This is the Peukert effect, and it is what most runtime calculators quietly ignore. LiFePO4 lithium barely feels it, staying near its full capacity at almost any rate. This tool applies the derate only to lead-acid and only to the hours-at-a-heavy-load figure; gentle daily loads like a fridge sit far below the 20-hour rate, so the days figure is unaffected.

Step 4: Cold weather shrinks the bank too

Capacity falls as the battery gets cold. Near freezing, a lead-acid bank gives roughly 20 to 25% less than its rating and a lithium bank around 10% less; in hard cold both can drop toward half. Tick the cold-weather option and the tool trims usable capacity accordingly. A separate warning for lithium owners: you can discharge a LiFePO4 battery in the cold, but you must never charge it below freezing without an internal heater, or you damage the cells.

Step 5: Runtime is only half the story: you have to recharge

This tool tells you how long a full bank lasts. Boondocking (camping off-grid) for longer than that means putting back what you draw each day, from solar, the alternator through a DC-DC charger, or shore power. If your runtime is shorter than you would like, the fix is either a bigger bank or faster charging, and our RV Solar & Battery Calculator sizes the solar array and charge controller to replace your daily draw. Treat this number as how long you can coast, not how long you can live there.

Typical RV 12V load reference

Representative draws for common RV and van equipment, the same figures the tool starts from. Your own gear varies, so check the label where you can. The 12V compressor fridge is almost always the biggest single house load.

Device Amps (12V) Typical hrs/day
12V compressor fridge 4 10
Roof vent fan (MaxxFan / Fan-Tastic) 2.5 6
LED interior lights 2 4
Fresh-water pump 5 0.5
Phone and laptop charging 3.5 3
Propane / CO detector 0.1 24
Propane furnace blower fan 6 2
Diesel air heater 1 4
Starlink (12V) 4.5 5
12V LED TV 3 3
12V circulation fan 1.5 4
12V stereo / speaker 2 2

Need more runtime? Here is the gear

The two levers are a bigger or better bank and faster charging. Here is what we trust for each.

Planning a system from scratch, or sizing the solar to recharge it? Use the RV Solar & Battery Calculator, which works the other direction: your loads to the bank, solar, and charge controller you need.

How we are paid: some links above go to Amazon, and if you buy through them we earn a commission at no extra cost to you. It does not change what we recommend.

Common questions

How long will a 100Ah battery run my 12V fridge?

Roughly 1.5 to 3 days on a 100Ah lithium battery, and about 1 to 2 days on a 100Ah lead-acid one, running only the fridge. A 12V compressor fridge draws around 4 amps duty-averaged, about 40 to 50 amp-hours a day, because the compressor only runs part of the time. A 100Ah lithium gives about 80 usable amp-hours (80% depth of discharge), so 80 divided by a typical 40 to 50 Ah/day is roughly 1.5 to 2 days; an efficient fridge in mild weather (closer to 25 Ah/day) stretches it toward 3. A 100Ah lead-acid gives only about 50 usable amp-hours, so closer to 1 day. The calculator above does this for your exact bank and loads.

How do I calculate how long my battery will last?

Take your usable capacity (bank amp-hours times the usable share, about 50% for lead-acid or 80% for lithium) and divide it by your daily draw in amp-hours (each 12V load's amps times the hours you run it). The result is days of runtime before you need to recharge. For a single heavy continuous load like an inverter, divide usable watt-hours by the load's watts to get hours, and for lead-acid trim that further for the Peukert effect. The tool does all of this from the loads you select.

Why won't a 100Ah battery give 100 amps for one hour?

Because the 100 amp-hour rating is measured at a slow 20-hour discharge, which is 5 amps for 20 hours, not 100 amps for 1 hour. Pull the current fast and a lead-acid battery delivers significantly less than its rating, the Peukert effect: around 25% less at the 5-hour rate and up to 40% less at a hard inverter draw. LiFePO4 lithium is far more linear and holds close to its rating at high currents, which is one reason it is preferred for running inverters.

Lead-acid or lithium: which lasts longer?

Lithium lasts longer from the same nameplate amp-hours, for two reasons. First, usable depth of discharge: lithium is planned to about 80% versus 50% for lead-acid, so a 100Ah lithium gives about 80 usable amp-hours against roughly 50 for lead-acid, around 1.6 times the runtime before you even account for anything else. Second, under heavy loads lead-acid loses more to the Peukert effect while lithium barely does, widening the gap further. Lithium also tolerates cold better. The trade is upfront cost.

Does cold weather reduce how long my battery lasts?

Yes. Battery capacity falls as temperature drops. Near freezing a lead-acid bank gives roughly 20 to 25% less than its rating and a lithium bank around 10% less, and in hard cold both can fall toward half their rated capacity. Tick the cold-weather option in the calculator to trim the estimate. One safety note for lithium: you can use (discharge) a LiFePO4 battery in the cold, but you must not charge it below freezing without a built-in heater, or the cells are damaged.

How do I make my battery last longer off-grid?

Two levers: draw less, or recharge faster. Switch the fridge to a more efficient model or shade it, run LED lights and a low-speed roof fan instead of an inverter, and kill phantom loads like an idling inverter. Then make sure you can replace what you use each day with solar, an alternator DC-DC charger, or shore power, because runtime alone runs out. A bigger bank buys more coasting time, but charging is what lets you stay out. Our RV Solar & Battery Calculator sizes the solar and charging to match your daily draw.

Disclaimer

This calculator is provided for general informational and educational purposes only and gives a planning estimate based on accepted battery sizing math as of 2026. It is not a measurement of your actual battery and not a substitute for a battery monitor or a qualified installer. Real runtime varies with battery age, health, and chemistry, temperature, the true draw of your equipment, inverter and wiring losses, and state of charge, and lead-acid capacity under load varies with the discharge rate (the Peukert effect). We make no warranty as to accuracy or fitness for any particular system. You are responsible for how you use and charge your batteries, and a LiFePO4 bank must never be charged below freezing without an internal heater. Last reviewed June 2026.

The Dispatch

New picks, when we publish them. No filler.

One short email when a guide goes up, no filler. We're setting it up now, so sign-up opens soon.

Sign-up opens soon