How to Size a Battery Bank for a Van or RV: Step-by-Step Walkthrough

The “what size battery bank?” question gets asked in the r/vandwellers and r/GoRVing subreddits roughly once a week, and almost every answer is wrong in the same way: people overshoot. They build a 600Ah bank for a use case that needs 200Ah, then complain six months later about cost and weight.

The right answer is almost always smaller than you think. This guide gives you the math to figure out the actual minimum size for your loads, the framework to add a sensible buffer on top of that, and four concrete recommendations at the most common capacity tiers — backed by hands-on testing of every battery I’ll mention.

Step 1: List Every Load in the Build

Before any math, write down everything that will draw from the battery bank. Be honest and complete. The most common reason van builds get under-sized is that someone forgot to include the inverter’s idle draw, the parasitic load from a Wi-Fi router, or the fridge’s daily cycling.

A typical van conversion has these loads:

• 12V compressor fridge — 30–60W when running, cycles 30–40% of the time. Average 20–30W continuous.
• LED ceiling and accent lights — 5–10W per fixture, used 4–6 hours per night.
• MaxxFan or roof vent fan — 3–10W on low, 30W on high. Often runs all day in summer.
• USB charging (phones, tablets, headlamp, drone) — 30–60W aggregate, 1–4 hours per day.
• Inverter idle draw — 8–25W whenever the inverter is “on” but no load is connected. Easily forgotten.
• Water pump — 50–80W when running. Total daily runtime usually under 10 minutes.
• 12V Wi-Fi router or cellular hotspot — 10–15W continuous if always on.
• Heating element loads — Diesel/propane heater fans (8–15W), induction cooktops (1,200–1,800W for short bursts), water heaters.

Things people forget that they shouldn’t:

• Phantom loads — every 12V outlet with a USB cube plugged in draws something.
• Refrigerator door opens — each open cycle costs an extra 5–10Wh as the compressor catches up.
• Cold-weather operation — a fridge in 90°F ambient draws 30–50% more than the same fridge at 65°F.

Step 2: Calculate Daily Watt-Hours

The formula is the same one used for home backup sizing:

Daily Wh = sum of (Watts × hours per day) across all loads, then add 15–20% for inverter and DC-DC overhead.

Here’s a worked example for a typical full-time van conversion in summer conditions:

That’s roughly 1,700Wh per day, or 140Ah per day at 12V for a typical full-time van.

For a weekend-only van without the always-on Wi-Fi and without a constantly-running fridge, the same calculation usually lands between 800–1,200Wh per day (65–100Ah).

For a Class C or Class A motorhome with TVs, larger fridges, an inverter running often, and full-time use, expect 2,500–4,500Wh per day (200–375Ah).

Step 3: Account for Solar Input

Battery bank size doesn’t have to cover 100% of your daily load if you have solar input refilling capacity during the day. For a van with 400W of rooftop solar in summer conditions, you typically harvest 1,500–2,500Wh per day. In winter, that drops to 400–900Wh per day depending on latitude and weather.

The honest math: solar covers most or all of your daily load in summer, and roughly half in winter. Size your battery bank to cover at least 1.5 days of consumption assuming zero solar input — that gives you the buffer to ride out storms, cloudy stretches, and parking under a tree.

For our 1,734Wh/day example: 1.5 days × 1,734Wh = 2,600Wh of usable capacity = 216Ah at 12V.

That’s how you arrive at “200Ah is the right size for a typical full-time van.” Not a guess. Math.

Step 4: Adjust for Depth of Discharge and Temperature

Two things change your usable capacity from the spec-sheet number:

Depth of discharge (DoD). LiFePO4 batteries can theoretically be discharged to 100% DoD without damage, but most builders set the inverter low-voltage cutoff at 90–95% DoD to leave a small reserve and extend cycle life. So a “200Ah” battery is realistically 180–190Ah of usable energy in daily use.

Temperature. LiFePO4 capacity drops about 10–15% in freezing temperatures, and most LiFePO4 batteries refuse to charge below 32°F (0°C) without a built-in heater. If you’ll be in winter conditions regularly, either:

• Buy a battery with a built-in heating function (the Epoch 460Ah is a good example), or
• Add an external heater pad (~$80) and insulate the battery compartment, or
• Plan to rely on shore power or vehicle-charging during cold weather.

For our worked example, a 200Ah single battery delivers ~190Ah usable in normal conditions, which still beats our 216Ah target by being close enough — buy two 100Ah batteries in parallel for 380Ah usable, or buy a single 200Ah, or step up to 280–300Ah for headroom. All three are defensible.

Step 5: Pick a Capacity Tier

Most van and RV builds fit one of three tiers cleanly. Here’s how to read them:

Tier 1: Weekend / Minimal (100–200Ah)

For a weekend van that just needs to run a small fridge, lights, and device charging, 100Ah of LiFePO4 is enough. With 200W of solar replenishing during the day, even four-day trips stay above 50% state of charge.

The single best value here is the Renogy 100Ah LiFePO4 at around $280. Built-in Bluetooth monitoring, IP65 rating for splash-resistant outdoor mounts, and a 5-year warranty hit a sweet spot for low-stakes weekend builds.

If you want premium reliability and don’t mind paying for it, the Battle Born 100Ah at $925 is the gold-standard 100Ah battery — 10-year warranty, US-based support, and a track record stretching back further than any other LiFePO4 brand. It’s overkill for a weekend van. It’s the right pick if your bank is going into a vehicle you’ll keep for 15+ years.

Tier 2: Full-Time Van / Mid-RV (200–400Ah)

This is the most common bracket. A full-time van or a moderately-equipped Class B/C usually lands here.

For full-time van use, a single 200Ah battery is the cleanest answer. One battery, one set of cables, one BMS, one Bluetooth signal. The LiTime 200Ah Plus at around $460 is the value pick — 200A BMS, built-in Bluetooth, IP65, 4,000-cycle rating. Roughly half the price-per-Ah of the premium alternatives.

For a slightly more ecosystem-integrated option, the Renogy 200Ah LiFePO4 at $600 fits well into builds that already use Renogy charge controllers and panels — the app monitors the whole system from one place.

If your daily load runs 2,500–3,000Wh per day (typical full-time van with heavy laptop work, induction cooking, or hair dryer use), step up to two 200Ah batteries in parallel for 400Ah / 5,120Wh of capacity. Buy them as a matched pair from the same vendor on the same date.

Tier 3: Big Build / Class A / Off-Grid RV (400Ah+)

For Class A motorhomes, big fifth wheels, off-grid-style mobile cabins, or any build with central HVAC ambitions, you’re past the point where stacking 100Ah/200Ah batteries makes sense.

The Epoch 460Ah at around $900 is the most cost-effective way to put 5,888Wh into a single battery. 7,000-cycle rating, 250A continuous discharge (enough to feed a 3,000W inverter), 10-year warranty, and built-in self-heating for cold-weather operation. The catch is the 94-lb weight and server-rack form factor — it doesn’t fit standard battery compartments.

For Class A builds where you want true whole-rig independence, two Epoch 460Ah batteries in parallel give you 11,776Wh of usable capacity — enough to run residential-style appliances, central-style HVAC, and overnight inverter loads without needing a generator or shore power refresh for several days.

Common Sizing Mistakes

After reading hundreds of build threads, these are the five mistakes I see most often:

1. Building for the upper bound of your load list. Most builders assume their hair dryer, induction cooktop, and microwave will all run together. They almost never do. Size for the realistic daily total, not the worst-case simultaneous draw.
2. Forgetting inverter idle draw. A 2,000W pure sine wave inverter idles at 15–25W. Over 24 hours that’s 360–600Wh — easily a quarter of a small bank’s daily capacity.
3. Sizing for full DoD on day one. Run your bank to 90% DoD daily and you’ll be replacing the battery in 6–8 years instead of 12–15. Build with headroom.
4. Mixing battery brands or ages in parallel. Two different batteries in parallel will pull each other down to the weaker battery’s performance. Always match brand, model, age, and state of charge.
5. Ignoring temperature. A bank that performs perfectly in 70°F garage conditions can lose 30% capacity at 25°F and refuse to charge below 32°F. If you’ll see real winter, plan for it from day one.

Final Recommendation

For most van and RV builders shopping for a battery bank in 2026:

• Weekend or minimal builds (under 1,200Wh/day): Renogy 100Ah LiFePO4, single battery. Add a second only if you outgrow it.
• Full-time van or moderate RV (1,200–2,500Wh/day): LiTime 200Ah Plus, single battery. The 200Ah-in-one-box approach beats two 100Ah batteries on cost, complexity, and reliability.
• Heavy-use full-time (2,500–4,000Wh/day): Two LiTime 200Ah Plus batteries in parallel for 400Ah / 5,120Wh.
• Class A / off-grid RV (4,000Wh+/day): Epoch 460Ah, one or two depending on need.

Whatever you pick, do the math first. Use the formula in Step 2 with your real load list, multiply by 1.5 to get target usable capacity, divide by 12V to get amp-hours, and add 10% for headroom. The number you get is almost always smaller than what you would have bought based on Reddit advice.

For more detail on specific sub-decisions, see our deep-dives on LiFePO4 chemistry, series vs parallel wiring, and amp-hours vs watt-hours. Or browse the full batteries category hub for tested picks across every form factor.