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RV Battery Bank Sizing Calculator

Calculate the right size house battery bank for your RV based on chemistry (LiFePO4, AGM, flooded), days of autonomy, and temperature.

Inputs

Modest RV: 50-100 Ah/day. Heavy use: 150-300+ Ah/day. Use our solar calculator to find Wh, then divide by 12.
How long you need to run with no recharge.
Different chemistries have very different usable capacity.
Cold weather reduces lead-acid capacity. LiFePO4 can't charge below 32°F without a heater.
Typical: 100Ah, 200Ah, 300Ah.

Battery sizing isn't just about Ah

The "100Ah battery" you see on the box is the manufacturer's rating under ideal lab conditions. In a real RV, you can only safely use a fraction of that — the rest stays in the battery to keep it healthy. This is called depth of discharge (DoD), and it's where most undersized RV electrical systems get into trouble.

ChemistryRecommended DoDTypical cycle lifePer usable Ah
LiFePO4 (lithium iron)80-90%3000-6000 cycles$$ (best long-term value)
AGM50%500-1000 cycles$ upfront / $$$ over life
Flooded lead-acid50%1000-1500 cycles$ (cheapest, requires maintenance)
Gel50%500-700 cycles$$ (rarely worth it)

Temperature matters more than you think

Lead-acid batteries lose roughly 20% of their usable capacity at 32°F and up to 50% at 0°F. Lithium iron phosphate (LiFePO4) holds capacity well in cold but cannot accept charge below freezing without an internal heater. Most quality lithium batteries now include built-in low-temp charging cutoffs and many include heating elements.

Series vs parallel

Two 100Ah 12V batteries wired in parallel give you 200Ah at 12V. Wired in series, they give you 100Ah at 24V. Most RV systems are 12V, so parallel is the default. If you're building a 24V or 48V system (common for higher-power off-grid setups), the math in the calculator still applies — just convert your Ah needs to the right voltage.

Frequently Asked Questions

How many amp-hours do I need?
Add up the Ah draw of every 12V device times the hours you run it daily. A 12V fridge averages about 30Ah/day. LED lights add 5-10Ah. A water pump used a few times a day adds maybe 2-5Ah. Charging laptops and phones via inverter adds another 10-20Ah. Most weekend campers land around 50-100Ah/day; full-timers with a residential fridge and lots of electronics push 200-400Ah.
Should I switch to lithium?
If you boondock often and your current bank is more than 5-7 years old, almost certainly yes. Lithium gives you ~2x usable capacity in the same weight, charges faster, lasts 5-10x as many cycles, and weighs less than half as much. The upfront cost is higher but cost-per-cycle is dramatically lower.
Can I mix old and new batteries?
Never mix chemistries (e.g., lead-acid with lithium). Within the same chemistry and voltage, mixing batteries of different ages or capacities is technically possible but reduces the usable capacity of the whole bank to the level of the weakest battery. If you have to mix, group same-age batteries on the same circuit.
How big a fuse do I need on the battery bank?
Right at the positive terminal, install a Class T or ANL fuse rated for the maximum continuous current your inverter can pull, plus margin. For a 2000W inverter at 12V, that's roughly 200-300A. Class T fuses are required for lithium because of the very high short-circuit current available.

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Want to understand the why behind these numbers? Read Boondocking Power Basics — the math behind amp-hours and depth of discharge.

About our math & sources

Every default and formula in this calculator is grounded in published manufacturer specs, industry standards, or peer-reviewed measurement. Where we make assumptions, we tell you what they are so you can adjust.

  • Depth of Discharge (DoD). LiFePO4: 80–90% (manufacturer specs from SOK, EG4, LiTime, Battle Born). Lead-acid: 50% (industry consensus to preserve cycle life). Going deeper is possible but cycle life drops dramatically.
  • Cycle life figures. Manufacturer-published cycles to 80% capacity at recommended DoD: LiFePO4 3,000–6,000; AGM 500–1,000; Flooded 1,000–1,500.
  • Temperature derating. Lead-acid loses ~0.6% capacity per °C below 25°C (Trojan, US Battery technical bulletins). LiFePO4 retains capacity better but cannot accept charge below 0°C without internal heating.
Disclaimer. This calculator provides estimates only. Real-world results depend on equipment efficiency, environmental conditions, and installation quality. Always verify against your equipment's spec sheets and consult a licensed installer for safety-critical decisions.