--- title: RV House Batteries [+Calculator] | Boondocking.ai description: RV house batteries, sized to your nights. Usable vs nameplate capacity, lithium vs AGM, cold-weather charging, plus a free calculator and FAQ. --- House batteries # RV house batteries, sized to your nights By [Justin Champion](https://boondocking.ai/about?hsLang=en)· Boondocked 200+ nights· Updated June 18, 2026 Most dead-battery nights aren't battery failures. They're sizing failures. People buy a bank off the number on the sticker, plan around the wrong half of it, and run out at 2am with the furnace fan still cycling. This is the comprehensive version: what your house batteries actually do off-grid, how to size the bank to the nights you actually camp, and a calculator that does the math on your setup. ## Key takeaways - **Usable, not nameplate.** Half of an AGM bank is off-limits before you damage it. Plan from the smaller number, always. - **The bank is the bottleneck.** Solar refills it, but the usable capacity is the thing that carries you through the night. - **Chemistry drives everything.** Lithium versus AGM changes your usable depth, your weight, your charge speed, and your lifetime cost. - **Cold is two separate problems.** Capacity drops as it gets cold, and lithium can't charge below freezing without a heater. - **Size for the cloudy stretch.** One day of usable margin is the floor. Two is comfort. ## The four numbers that size a battery bank Your bank is the tank. Solar, the alternator, and a generator are just hoses that fill it, and the whole game of boondocking power is keeping that tank from hitting empty before the next good charging window. Four numbers decide how big the tank needs to be, and they only work in this order. 01 Daily draw amp-hours / day What you pull from the bank in a day. 02 Usable depth % of nameplate How much of the rating you can actually use. 03 Days of autonomy nights of buffer How long you go without a full recharge. 04 Chemistry lithium / AGM What sets the depth, weight, and cost. ## Usable capacity is the number that matters Here's the part the spec sticker skips. A 100Ah battery is not 100 amp-hours of energy you get to use. Two numbers stand between the label and the power you can actually pull: how deep you can safely discharge it, and the losses on the way out. Depth of discharge is the big one, and chemistry sets it. AGM and flooded lead-acid should only be drawn down about 50% before damage starts, so a 100Ah AGM is really about 50Ah usable, good for roughly 300 to 600 cycles. LiFePO4 gives you 80 to 100% usable and 3,000 to 6,000 cycles, per the chemistry comparisons at [MANLY Battery](https://manlybattery.com/rv-camper-battery-lifespan-replacement-planning-agm-vs-lifepo4/) and [Battery Tender](https://www.batterytender.com/blogs/battery-tender-blog/battery-chemistry-comparison-agm-vs-lithium-lifepo4-vs-flooded-vs-gel). That single fact, usable versus nameplate, is behind most "my battery died way too fast" stories. | Chemistry | Usable depth | Cycle life | | --- | --- | --- | | LiFePO4 (lithium) | 80 to 100% | 3,000 to 6,000 | | AGM | ~50% | 300 to 600 | | Flooded lead-acid | ~50% | 300 to 500 | Then the smaller cut: inverters, wiring, and charge-discharge inefficiency skim roughly 10% off the top in a typical 12V system, and cold weather skims more. So when you size, you start from usable capacity and work backward to the nameplate you actually have to buy. ## How big does your bank need to be? Size the bank to carry your daily draw times the number of cloudy days you want to survive without the sun refilling it. One day of margin is the floor. Two is comfort. The math is simple: usable amp-hours needed equals your daily draw times your days of autonomy, then convert to the nameplate you have to buy by dividing by your usable depth and a small efficiency factor. Run realistic first-timer numbers. Say you pull 100 amp-hours on a normal day and you want a two-day cushion. That's 200 usable amp-hours to keep on hand. In LiFePO4 at 80% usable, that's about a 300Ah nameplate bank. In AGM at 50% usable, the same 200 usable amp-hours needs roughly 450Ah of nameplate, and AGM weighs about twice as much per amp-hour, so you've added a few hundred pounds to carry the same usable power. That comparison is the whole argument for lithium. The calculator below does this against your real rig, loads, and climate, and hands the number straight to the chemistry decision. ## Lithium vs. AGM vs. flooded Chemistry isn't a detail you bolt on at the end. It sets your usable capacity, your weight, your charging hardware, and your cost over the life of the rig. **Lithium iron phosphate (LiFePO4)** is the default for serious boondocking, and it isn't close: 80% usable depth instead of 50%, roughly a third of the weight per usable amp-hour, a flat voltage curve that keeps your 12V gear happy down to near-empty, and several thousand cycles. It takes a charge fast, too. The catch is upfront cost, and one real limit: most cells can't be charged below freezing without a heater. **AGM** is a sealed, maintenance-free lead-acid battery. Cheaper to buy and tolerant of imperfect charging, genuinely fine for light or occasional use, but you live with 50% usable depth, real weight, shorter cycle life, and slow charge acceptance that wastes solar and generator runtime. **Flooded lead-acid** is cheapest to buy and the most work to own: watering, venting, and real sensitivity to being left part-charged. Lithium looks expensive until you divide by usable cycles. Over the life of the rig it's usually the cheaper battery, because you buy one bank instead of replacing lead-acid two or three times. ## Cold weather, charge acceptance, and the tradeoffs nobody mentions **Charge acceptance is the hidden bottleneck.** Lead-acid only takes a charge so fast and tapers hard as it fills, so the last 20% can take hours, and a big array or a generator spends much of its time throttled by what the battery will accept. Lithium takes a high, steady charge almost to full, so the same panels and generator put far more back in the same window. **Cold is two problems.** Capacity drops for every chemistry as it gets cold, and charging LiFePO4 below about 32°F damages the cells, so you want a battery with a built-in heater, a warmed bay, or the discipline to wait until it warms above freezing. **Your charger has to match your chemistry.** Owners who've made the jump back this up. In one [Airstream Forums upgrade thread](https://www.airforums.com/threads/upgrading-from-agm-to-lithium-batteries.1412003/), the repeated advice on a lithium swap is to replace the converter for a lithium profile and add a DC-DC charger for the tow vehicle, since a truck's roughly 13-volt charging won't fully fill a lithium bank. The owner who started it had already ruined a set of AGMs through mismatched charging, and the group's math was blunt: a couple hundred dollars for the right charger is cheap insurance on a two-thousand-dollar bank. From the Airstream forums One owner with a lithium bank and five solar panels ran the furnace two nights running, sure the capacity made the draw irrelevant. On the third morning the readout was dead, the bank had sagged to 10.47 volts, and there wasn't enough left to spark the stove for coffee. They ended up heating water on the outdoor grill. The fix they landed on is the one this page is built around: learn what each load actually pulls before you commit to a site, and treat the furnace fan as a real overnight cost. A line that runs through that whole thread is worth keeping: a battery is reserve, not a power source. It stores energy, it doesn't make it. Paraphrased from a [boondocking-on-lithium thread](https://www.airforums.com/threads/boondocking-on-lithium-batteries.1428969/) on the Airstream Forums. ## Run your numbers Battery calculator ## Size your bank in about 60 seconds Tell us your rig, your daily amp-hour target, and how cold the bay gets. We'll pick the chemistry and the nameplate size your real setup needs, break out how much you can actually use, and point you at the generator math. Power · boondocking.ai ## Battery calculator We've got your daily Ah from Solar. Tell us how cold the bay gets, and we'll pick the chemistry and the size that actually fit. Tell us your rig, your daily Ah target, and how cold the bay gets. We'll pick the chemistry and the size that actually fit. About 60 seconds. Section 1 of 3 ### Your rig Pre-filled from your Solar inputs. Change it if you're sizing for a different rig. Pick the closest match. We use this to set realistic defaults. Class A Class B Class C Travel trailer 5th wheel Van or other People on board − + Section 2 of 3 ### Your daily Ah target From your Solar result. The bank gets sized to cover this. The bank gets sized to cover this for the days of reserve you pick. 200Ah usable Pre-filled value. Use a different number [ Run Solar first → ](https://boondocking.ai/rv-solar-power?return_to=battery&hsLang=en) or Hand-enter the target − + Default reflects your rig. Bump it if you run more. Plan for more reserve (default 1 day) Section 3 of 3 ### How cold does the bay get? LiFePO4 won't accept charge below freezing. AGM doesn't care. This shapes the recommendation. Mild Cold Below freezing **Mild.** Bay rarely below 40°F. LiFePO4 charges normally. Pick this if you boondock spring-through-fall or stay south in winter. Size my battery Power · boondocking.ai ## Your Battery result 2 of 3 toward your readout Class B · 2 adults · mild bay · 1 day reserve 280Ah nameplate LiFePO4drop-in LiFePO4 fits your bay temp, hits 200Ah usable in a single 280Ah pack, and trades roughly $1,000 upfront for about five times the cycle life of AGM. Compare AGM → Bank usable 200 Ah Daily draw −72 Ah End-of-day reserve 128 Ah Next step ### Cover the cloudy week Your bank carries one full day. The Generator calculator sizes the backup for the cloudy stretch. [Start the Generator calculator → ](https://boondocking.ai/rv-house-batteries#) Class B, 200Ah from Solar, mild bay, 1 day reserve. Edit Share Start over One more calculator and your **readout** unlocks. The next one gets you there. [Start the Generator calculator → ](https://boondocking.ai/rv-house-batteries#) ## The mistakes that leave you rationing a dead bank **Sizing by the label instead of the usable number.** "I have 200 amp-hours" means 100 usable in AGM, and the bank quits halfway through the night. **Buying lead-acid to save money.** Lower sticker, higher lifetime cost once you count replacements. **Skipping the cold plan.** Lithium taken into the mountains in October won't charge in the morning. **Ignoring the furnace and inverter draw.** The blower and an always-on inverter pull far more overnight than the lights people plan around. **Oversizing solar to rescue an undersized bank.** Panels can't store energy overnight, only the battery can. If the nights are the problem, more panel isn't the fix. ## RV house batteries, frequently asked How many batteries do I need to boondock? It depends on your daily amp-hour draw and how many cloudy days you want to survive, not on a one-size number. A weekend rig pulling 60 to 100 amp-hours a day usually needs about 200 usable amp-hours for a one-day cushion, which is roughly 200 to 250Ah of LiFePO4 or about 400Ah of AGM. Run the calculator above for your actual setup. What's the difference between usable and nameplate capacity? Nameplate is the number on the label. Usable is what you can pull without damaging the battery. AGM gives back about 50% of nameplate, LiFePO4 about 80 to 100%. A "200Ah" bank is either 100 usable amp-hours (AGM) or about 160 to 200 (lithium), and your trip planning has to use the smaller number. Lithium or AGM for boondocking? For anyone boondocking regularly, lithium. You get more usable capacity per pound, faster charging, and several times the cycle life, which makes it cheaper over the life of the rig despite the higher sticker. AGM is fine for occasional, light off-grid use where the upfront cost matters most. How long will a 100Ah battery last off-grid? Plan on roughly 40 to 50 usable amp-hours from a 100Ah AGM and 80 from a 100Ah lithium. Against a typical 60 to 100 amp-hour day, a single 100Ah lithium is most of one modest night and a single AGM is about half. That's why most rigs run two or more. Can I charge a lithium battery in freezing weather? Not safely, unless it's built for it. Charging standard LiFePO4 below about 32°F damages the cells. Buy a battery with a built-in heater and low-temp cutoff, warm the bay, or wait until it's above freezing to charge. Discharging in the cold is fine; charging is the problem. How many amp-hours do I use in a day? Most weekend boondockers without AC or induction run 60 to 100 amp-hours a day, and the 12V fridge is usually more than half of it. The only way to know your real number is to watch a shunt-based battery monitor for a few normal days. It's the most useful $100 to $200 you'll spend on the rig. Do I really need a battery monitor? Yes. Voltage alone is a poor gauge of a lithium bank's state of charge because the voltage curve is so flat. A shunt monitor shows real amp-hours in and out and tells you what you actually draw, which is the input every sizing decision depends on. Will adding more solar fix my dead-battery problem? Only if your days are the problem. If you start the evening full and still hit empty by morning, the bank is too small and no amount of daytime charging fixes it. Size the battery for the night first, then size solar to refill it. Your next number ### Next: what size generator do you need? You'll know your bank size and chemistry. The Generator calculator sizes the generator your rig actually needs, set by the startup surge, usually the AC, and tells you whether you even need one. About 90 seconds. [Start the Generator calculator →](https://boondocking.ai/rv-generator?from=battery&hsLang=en) Sources: battery chemistry, depth of discharge, and cycle life from [MANLY Battery](https://manlybattery.com/rv-camper-battery-lifespan-replacement-planning-agm-vs-lifepo4/) and [Battery Tender](https://www.batterytender.com/blogs/battery-tender-blog/battery-chemistry-comparison-agm-vs-lithium-lifepo4-vs-flooded-vs-gel). Lithium-conversion and charger-matching patterns from the [Airstream Forums AGM-to-lithium thread](https://www.airforums.com/threads/upgrading-from-agm-to-lithium-batteries.1412003/) and [boondocking-on-lithium thread](https://www.airforums.com/threads/boondocking-on-lithium-batteries.1428969/). ```json { "@context" : "https://schema.org", "@id" : "https://boondocking.ai/#organization", "@type" : "Organization", "founder" : { "@id" : "https://boondocking.ai/about#person" }, "logo" : "https://452474.fs1.hubspotusercontent-na1.net/hubfs/452474/favicon-512.png", "name" : "boondocking.ai", "publishingPrinciples" : "https://boondocking.ai/about#editorial-process", "sameAs" : [ "https://www.instagram.com/wildwewander/" ], "url" : "https://boondocking.ai" } ``` ```json { "@context" : "https://schema.org", "@type" : "FAQPage", "mainEntity" : [ { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "It depends on your daily amp-hour draw and how many cloudy days you want to survive. A weekend rig pulling 60 to 100 amp-hours a day usually needs about 200 usable amp-hours for a one-day cushion, roughly 200 to 250Ah of LiFePO4 or about 400Ah of AGM." }, "name" : "How many batteries do I need to boondock?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "Nameplate is the label number. Usable is what you can pull without damage. AGM gives back about 50%, LiFePO4 about 80 to 100%. A 200Ah bank is either 100 usable amp-hours in AGM or about 160 to 200 in lithium, and planning has to use the smaller number." }, "name" : "What is the difference between usable and nameplate battery capacity?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "For regular boondocking, lithium. More usable capacity per pound, faster charging, and several times the cycle life make it cheaper over the life of the rig despite the higher sticker. AGM is fine for occasional, light off-grid use where upfront cost matters most." }, "name" : "Lithium or AGM for boondocking?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "Plan on roughly 40 to 50 usable amp-hours from a 100Ah AGM and 80 from a 100Ah lithium. Against a typical 60 to 100 amp-hour day, a single lithium is most of one modest night and a single AGM about half, which is why most rigs run two or more." }, "name" : "How long will a 100Ah battery last off-grid?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "Not safely unless it is built for it. Charging standard LiFePO4 below about 32F damages the cells. Use a battery with a built-in heater and low-temp cutoff, warm the bay, or wait until it is above freezing. Discharging in the cold is fine." }, "name" : "Can I charge a lithium battery in freezing weather?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "Most weekend boondockers without AC or induction run 60 to 100 amp-hours a day, and the 12V fridge is usually more than half of it. The only way to know your real number is to watch a shunt-based battery monitor for a few normal days." }, "name" : "How many amp-hours do I use in a day?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "Yes. Voltage alone is a poor gauge of a lithium bank's state of charge because the voltage curve is flat. A shunt monitor shows real amp-hours in and out and tells you what you actually draw, which is the input every sizing decision depends on." }, "name" : "Do I really need a battery monitor?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "Only if your days are the problem. If you start the evening full and still hit empty by morning, the bank is too small and no amount of daytime charging fixes it. Size the battery for the night first, then size solar to refill it." }, "name" : "Will adding more solar fix my dead battery problem?" } ] } ```