Van House Battery Guide (US): LiFePO4 Sizing & Wiring 2026

Your house battery — also called the auxiliary or "coach" battery — is the heart of a van or RV electrical system. Every other component decision flows from it: how much solar you need, what DC-DC charger to buy, whether an inverter is practical. Size it right and you'll have worry-free power for years. Size it wrong and you'll be running for a generator on night two.

This guide covers battery chemistry in depth, sizing methodology with worked examples, US product comparisons with 2026 pricing, wiring configurations, installation, monitoring, and everything that goes wrong and why.

For how the battery fits into the full system, see our complete van electrical system guide.

Battery Chemistry: What You're Actually Buying

LiFePO4 (Lithium Iron Phosphate) — The Standard for Van Builds

LiFePO4 became the default choice for van and RV house batteries for good reason: it's chemically stable, has the best cycle life of any practical battery chemistry, and actually costs less over time than AGM despite higher upfront cost.

Unlike NMC (nickel manganese cobalt) chemistry used in laptop batteries and early EVs, LiFePO4 doesn't undergo thermal runaway — the self-reinforcing overheating that causes lithium battery fires. This is why LiFePO4 is approved for enclosed spaces in marine and RV applications.

Key specs:

The usable capacity difference is what really matters in practice. A 200Ah AGM gives you about 100Ah usable (50% DoD limit). A 100Ah LiFePO4 gives you 80–100Ah usable — similar storage from half the nominal capacity, at roughly 30–40% of the weight.

The 5-year cost analysis:

A quality 200Ah AGM at $200 lasts perhaps 400 cycles before significant capacity loss. At one cycle per day (typical full-time van life), that's ~13 months before replacement. Five years = 4–5 replacements = $800–$1,000 in batteries.

A quality 200Ah LiFePO4 at $500 lasts 3,000+ cycles — more than 8 years at daily use. Five-year cost: $500.

For any van that sees regular use, LiFePO4 is cheaper over the ownership period. The math gets even clearer when you factor in the weight savings and the smaller battery bank needed (since you use 80% of rated capacity instead of 50%).

AGM (Absorbent Glass Mat)

AGM is sealed lead-acid with the electrolyte absorbed in glass mat separators, making it spill-proof and maintenance-free. It was the standard for RV house batteries before LiFePO4 prices dropped to practical levels.

The 50% depth-of-discharge limit is the main constraint. Regularly discharging AGM below 50% accelerates sulfation — a progressive capacity loss from lead sulfate crystal buildup on the plates that's only partially reversible. An AGM battery you've discharged to 20% repeatedly will be significantly weaker within months.

AGM still makes sense for:

• A budget first build where you'll upgrade in a year or two
• RVs or campervans used only a few times a year where the lower cycle life isn't a factor
• Systems where someone already has AGM charging equipment

For anything used more than monthly, LiFePO4 is the right choice in 2026.

Understanding Battery Capacity

Battery capacity is rated in amp-hours (Ah) — the amount of charge a battery can deliver. A 100Ah battery can theoretically deliver 1A for 100 hours, or 10A for 10 hours.

More useful for van life planning: convert everything to watt-hours (Wh).

Conversion: Wh = Ah × voltage (use 12.8V for LiFePO4 nominal)

A 200Ah LiFePO4 at 12.8V nominal: 200 × 12.8 = 2,560Wh total, 2,048Wh usable (at 80% DoD).

Why watt-hours? Because you can directly compare battery storage to appliance consumption. A fridge that draws 50W for 20 hours consumes 1,000Wh — regardless of whether it's 12V or 120V.

The Peukert effect:

Battery capacity is affected by discharge rate — discharge faster and you get fewer amp-hours. LiFePO4 is nearly immune to this (Peukert exponent close to 1.0). AGM suffers meaningfully: a 100Ah AGM discharged at 20A might only deliver 85Ah before hitting the 50% SoC cutoff, rather than the theoretical 100Ah.

Sizing Your Battery Bank: The Methodology

Step 1: Calculate Your Daily Energy Budget (Wh/day)

List every appliance, its wattage, and how many hours per day you actually use it. Don't guess — look at spec sheets or measure with a clamp meter.

Example: full-time van build, four seasons

Notes on specific loads:

• Fridge: The biggest variable. The 45W average is for a well-insulated 12V compressor fridge at 70°F ambient. In summer heat (90°F in a van) it might average 70–80W. In winter cold, 25–35W. Use 50W average if uncertain.
• Diesel heater: Fan runs continuously at low watts; glow plug (80–100W) fires for only 2–3 minutes at startup. If your heater starts once per evening, add about 4Wh for the startup event — negligible.
• Laptop: If your laptop charges over USB-C, it charges at similar efficiency from a 12V USB-C PD charger as from 120V through an inverter. Use the actual laptop power consumption, not the charger's rated watts.

Step 2: Choose Your Autonomy Target

Autonomy is how many days you want to run without any charging source. More autonomy = larger (and more expensive) battery. The right answer depends on your travel style:

For most US van lifers, 2 days of autonomy with 300–400W of solar is the right balance.

Step 3: Calculate Required Capacity

Formula: Required Ah = (Daily Wh × Days autonomy) ÷ Nominal voltage ÷ Usable DoD

For LiFePO4 (80% usable DoD): = (1,906 × 2) ÷ 12.8 ÷ 0.80 = 372Ah → round to 400Ah (two 200Ah batteries in parallel)

For 1-day autonomy: = 1,906 ÷ 12.8 ÷ 0.80 = 186Ah → a single 200Ah LiFePO4

For AGM (50% usable DoD), 1-day autonomy: = 1,906 ÷ 12.8 ÷ 0.50 = 298Ah → three 100Ah or two 150Ah AGM batteries

This illustrates the AGM sizing penalty: more nominal capacity required, at higher weight, to deliver the same usable Wh.

Step 4: Account for Inverter Loads

If you'll run 120V appliances through an inverter, include their consumption in your daily budget. Inverters are approximately 85–90% efficient.

Battery draw for inverter loads: = Appliance watts ÷ inverter efficiency ÷ 12.8V = amps drawn from battery

Example: Making coffee with a Nespresso machine (1,100W) twice a day, 1 minute per cup: = 1,100W × (2 minutes ÷ 60) ÷ 0.88 efficiency = 41.7Wh from battery per day

A hair dryer (1,200W) for 8 minutes daily: = 1,200W × (8 ÷ 60) ÷ 0.88 = 181Wh from battery per day

Add these to your daily total before sizing the battery.

US Product Guide: Best House Batteries 2026

Budget Tier: LiTime and Ampere Time

LiTime (formerly Amperetime) has established itself as the best value option in the US market. They use Grade A prismatic cells (typically EVE), 100A built-in BMS, and offer strong specs at prices 60–70% below premium brands.

The LiTime 200Ah is exceptional value — close to 200Ah of usable capacity at under $400. The warranty is 5 years, and support is US-based.

Limitation: No low-temperature charge protection built in. The BMS doesn't automatically prevent charging below 32°F. At winter temperatures, you need to either prevent charging from happening (solar controller low-temp setting, etc.) or choose a self-heating model.

Mid-Range Tier: Renogy and SOK

Renogy Smart Lithium:

Renogy's Smart series adds Bluetooth monitoring and a low-temperature cutoff. The Renogy 12V 100Ah Smart LiFePO4 (~$259) prevents charging below 32°F automatically and shows cell-level voltage data through the Renogy app.

SOK Battery:

SOK (same factory as some other brands) offers 100A continuous BMS, good build quality, and is popular in the van life DIY community. The SOK 206Ah (~$449) is a popular choice for builds that want more than 200Ah without going to two batteries.

Premium Tier: Battle Born

Battle Born Batteries (made in the US, assembled in Reno, NV) are the reference standard for reliability. The 100Ah Heated ($849–$949) includes a proprietary self-heating element that warms the cells to charging temperature before allowing charge — the most reliable solution for all-season use.

The 10-year warranty and US-based support are genuinely valuable for full-time van lifers who can't afford downtime. Battle Born has the longest track record in the van life community and the most user data behind them.

Premium Tier: Victron SmartLithium

Victron's LiFePO4 batteries integrate natively with their ecosystem of MPPT controllers, DC-DC chargers, and monitoring systems.

The native Victron communication (VE.Bus) allows the battery to report its exact state of charge to a Cerbo GX, which coordinates charging from all sources. For full Victron ecosystem builds, the SmartLithium is the right choice.

Choosing Between Tiers

Go budget (LiTime, Ampere Time) if: You're building a first van, camping in temperatures above 40°F, and want to maximize Ah per dollar. Budget for replacement after 5–7 years rather than 10+.

Go mid-range (Renogy Smart, SOK) if: You want Bluetooth monitoring and low-temp protection without paying premium brand prices.

Go premium (Battle Born, Victron) if: You're full-timing year-round including winter, you want the longest reliable service life, or you're building a full Victron ecosystem.

Inside the BMS: What It Does and Why It Matters

Every LiFePO4 battery requires a Battery Management System (BMS). Without one, LiFePO4 cells are actually dangerous — they can over-charge or over-discharge to failure.

What the BMS does:

Cell balancing: Individual cells within a battery drift slightly in capacity over cycles. A prismatic 200Ah battery has four 50Ah cells in series. If one cell ages faster and has slightly lower capacity, it will hit 100% charge before the others — and get overcharged while the other cells are still charging. The BMS applies a small balancing current to equalize cells, either by dissipating excess energy (passive balancing) or redistributing it (active balancing).

Over-voltage protection: Cuts charging if any cell exceeds 3.65V. Overcharging LiFePO4 past this point causes capacity loss and potential cell failure.

Under-voltage protection: Cuts discharge if any cell drops below 2.5–2.8V. Over-discharging causes irreversible capacity loss.

Over-current protection: Disconnects if discharge current exceeds the BMS rating. A 100A BMS on a 100Ah battery means you cannot draw more than 100A continuously without triggering a disconnect.

Short-circuit protection: Disconnects within microseconds of a dead short. Critical — LiFePO4 can deliver thousands of amps into a fault.

Temperature protection: Disconnects charging below 32°F (0°C) on most quality batteries. This is the most important cold-weather protection.

When the BMS trips:

If your battery suddenly cuts out, the BMS has triggered a protection. Most common causes: over-discharge (battery hit its low-voltage cutoff), over-temperature, or a momentary overcurrent event (a large motor starting). To reset, apply a charging voltage — connect shore power, start the engine with DC-DC charger active, or ensure solar is producing. The BMS auto-resets when it detects a valid charging voltage.

A BMS that trips repeatedly has a real underlying cause — see the troubleshooting section.

Battery Bank Configurations

Single Battery

Simplest setup. All charge sources and loads connect to one battery. Works for most van builds.

Parallel (Higher Capacity)

Two or more identical batteries wired positive-to-positive and negative-to-negative. Doubles (or triples) capacity while keeping 12V nominal voltage.

Rules for parallel wiring:

1. Identical batteries only — same manufacturer, model, capacity, and ideally production batch. Mixing chemistries (AGM + LiFePO4) causes large equalisation currents that can damage both batteries. Mixing different capacities causes unequal loading.
2. Equal cable lengths from each battery to the bus bar. Different cable lengths mean different resistance, which means one battery does more work than the other. Wire them symmetrically.
3. Main positive and negative from diagonally opposite corners. For a two-battery bank, take the positive lead from battery 1's positive terminal and the negative lead from battery 2's negative terminal. This forces current to flow evenly through both batteries.

Two batteries with internal BMS can be paralleled safely — each BMS monitors its own cells and will disconnect if needed.

Series (24V System)

Two 12V batteries wired positive-to-negative produces 24V at the same Ah. Only consider 24V if your bank exceeds 400Ah (at 24V, lower current means thinner cables) or your inverter exceeds 2,000W (24V inverter cables carry half the current of 12V).

For most vans under 300Ah, 12V is simpler and correct.

Wiring the House Battery: Cables and Fusing

Main Battery Cable (AWG)

The main positive cable between the battery and the positive bus bar carries the entire system's current. Sizing in AWG:

Use fine-stranded, marine-grade, tinned-copper wire. Marine grade (ABYC E-11 compliant) is specified for its corrosion resistance and vibration tolerance — far superior to solid-core household wire or un-tinned automotive wire.

The Main Fuse: Use a Class T for LiFePO4

LiFePO4 batteries can deliver very high short-circuit current — 1,000A+ from a large bank. Standard ANL fuses are rated for interrupt currents of 6,000–10,000A. Class T fuses are rated for 20,000A interrupt current.

For LiFePO4 main battery fuses, use a Class T fuse (200A, 300A, or 400A depending on cable size), placed within 18 inches (ideally closer) of the battery's positive terminal. This is an ABYC recommendation for lithium batteries.

For AGM batteries, a standard ANL fuse is acceptable.

Battery Disconnect Switch

Install a manual battery disconnect (Blue Sea Systems, Victron) between the battery positive and the main fuse, or between the fuse and the bus bar. This lets you isolate the battery entirely for:

• Storage when the van isn't in use
• Emergency shutoff if a fault develops
• Working on the electrical system safely

Blue Sea Systems 5511e (amphibious disconnect, good for 12V DC) or the Victron Battery Protect are both solid choices.

Battery Monitoring: The SmartShunt

You cannot accurately determine LiFePO4 state of charge from voltage alone. The discharge curve is nearly flat — the battery holds around 13.2V from 90% SoC down to about 10% SoC. Voltage is almost useless as an SoC indicator until the battery is nearly empty.

A battery monitor (coulomb counter) tracks every amp flowing in and out, integrating over time to calculate true SoC. It's essential for informed power management.

Victron SmartShunt 500A (~$120):

A precision shunt resistor is inserted in the main negative cable between the battery negative terminal and the negative bus bar. Every amp that enters or leaves the battery passes through the shunt. The SmartShunt measures voltage across the shunt to calculate current, integrates that to track amp-hours, and computes SoC. Connects via Bluetooth to the Victron Connect app.

Installation:

The SmartShunt is the only thing that can be in the main negative cable between battery and bus bar. All negative returns must go to the bus bar, not directly to the battery — otherwise the shunt misses some of the current and gives wrong readings.

Key settings to configure in Victron Connect:

• Battery capacity: Set to your battery's actual rated Ah
• Charged voltage: The voltage at which the battery is considered 100% (set to your charger's absorption voltage, typically 14.2V for LiFePO4)
• Tail current: The current level at which the battery is considered full (4% of capacity — 8A for a 200Ah battery)
• Peukert exponent: 1.05 for LiFePO4 (nearly 1.0 — the Peukert effect is minimal)

Alternative: Renogy ONE M5 battery monitor (~$80) is a reasonable budget option for non-Victron builds.

Charging Profiles: Getting LiFePO4 Right

LiFePO4 charges in two stages:

Bulk phase: Charger delivers maximum current until cell voltage reaches the absorption voltage (~14.2–14.4V for a 12V pack). Charges the battery to ~95%.

Absorption phase: Charger holds the absorption voltage while current tapers as the battery fills. Ends when current drops to the tail current threshold.

Float phase: LiFePO4 does not need a float charge. Many quality chargers and MPPT controllers have a dedicated LiFePO4 mode that either disables float or sets it very low (13.5V) just to offset self-discharge. Never apply the AGM absorption voltage (14.4–14.7V) or equalization voltage to LiFePO4.

Required charger settings:

Cold-Weather Charging: The Critical Limit

Charging LiFePO4 below 32°F (0°C) causes lithium plating on the graphite anode — a permanent and potentially dangerous degradation mechanism. Each cold-charge event permanently reduces capacity and can eventually create internal shorts.

Protection strategies:

1. BMS with low-temperature charge cutoff: Most quality batteries (Battle Born, Renogy Smart, Victron SmartLithium) have BMS-level protection that disconnects charging below 32°F. The most reliable approach — no configuration needed.

2. Self-heating batteries: The Battle Born Heated series and similar products have a resistive heating element powered by the battery itself. When the BMS detects temperature below 23°F (-5°C), it activates the heater before allowing charging. Adds $50–$100 to the cost but eliminates the cold-weather constraint.

3. MPPT controller low-temperature cutoff: The Victron SmartSolar MPPT controllers can accept a temperature sensor input (separate accessory) and stop solar charging below a set temperature. Configure to 40°F to ensure charging only happens when cells are safely above 32°F.

4. DC-DC charger temperature sensor: Victron Orion-Tr Smart chargers support temperature compensation and cutoff with the appropriate sensor.

If your battery doesn't have low-temp protection built in:

Ensure the solar controller has a temp sensor and configured cutoff. Park the van so the battery is in a location that stays above freezing (inside the van, insulated from the floor). Charge from a wall outlet (indoors if possible) rather than solar on days below 32°F. For winter full-timing, investing in a self-heating battery is worthwhile.

Winterizing Your Battery

LiFePO4 winter storage (van off the road):

1. Discharge to approximately 50–60% SoC (resting voltage ~13.2–13.3V at 12V)
2. Disconnect from all loads and chargers
3. Store anywhere above -4°F (-20°C) — cold storage does not damage LiFePO4
4. No maintenance charger needed — 1–3% monthly self-discharge means a battery stored at 55% SoC will still be usable after months of storage
5. In spring, charge fully and do a calibration cycle (charge to 100%, discharge to 20%, recharge)

AGM winter storage:

AGM requires more attention. Charge fully before storage (14.4–14.7V absorption until current tapers to under 2A). Connect a desulfation-mode maintenance charger (NOCO Genius, CTEK) to compensate for the 3–5% monthly self-discharge. Check voltage every 6 weeks; recharge if below 12.4V. Keep above 32°F — a deeply discharged AGM can freeze at 14°F (-10°C), cracking the plates.

Troubleshooting

Battery draining overnight with nothing running:

Measure quiescent current with a clamp meter on the main negative cable. Above 50mA (0.05A) with everything switched off indicates a parasitic drain. Common culprits: inverter on standby (10–25W), fridge on its own internal timer, MPPT controller (typically less than 10mA — rarely the issue), radio or dash components drawing through the chassis ground.

BMS trips under heavy load:

The BMS is detecting an overcurrent event. Either the load genuinely exceeds the BMS's current rating, or a motor startup surge is exceeding the BMS's instantaneous limit. Measure actual current draw with a clamp meter. If you're genuinely exceeding the BMS limit, you need a battery with a higher-rated BMS, or to limit simultaneous loads.

Battery monitor showing wrong state of charge:

Battery monitors drift, especially after deep discharge or over-charge events. Recalibrate: charge the battery to 100% (complete absorption phase with current tapered to the tail threshold), then reset the monitor to 100%. The monitor starts recounting from a known reference point.

Batteries in parallel not sharing load equally:

Verify cable lengths are equal from each battery to the bus bar. Check that both batteries are the same SoC before connecting them in parallel (if one is at 90% and the other at 50%, large equalisation current flows until they match). Verify both batteries are the same model and age.

Battery won't accept charge after sitting over winter:

If the battery discharged below the BMS low-voltage cutoff over winter (especially if stored without disconnecting from a load), the BMS may be in a deep-sleep protection mode. Most quality batteries have a "wake-up" charge current the BMS will accept even from deep sleep — try connecting a charger and waiting 30 minutes before assuming the battery is failed.

Related Guides

• Van solar setup guide — recharge from the sun
• Van charging systems guide — DC-DC and shore power
• Van wiring & safety guide — AWG sizing and fuses
• Van inverters & 120V power guide — running household appliances
• Complete van electrical system guide — the full picture

FAQ

What size house battery do I need for a van?

For a weekender (fridge, lights, USB charging): 100–150Ah LiFePO4 is usually plenty. For full-time van life with a laptop and moderate loads: 200Ah LiFePO4 is the sweet spot. For induction cooking or air conditioning: 300Ah+. Use the sizing calculation above or our free calculator for a precise figure based on your actual appliances.

LiFePO4 vs AGM — which should I buy?

For any van used more than a couple of times per month, LiFePO4. The higher upfront cost is recovered in 2–3 years through longer service life, you get more usable capacity per pound, and the weight savings improve handling and fuel economy. AGM only makes sense for a bare-budget build you plan to upgrade soon.

Can I use a car battery as a house battery?

No. Starter batteries deliver very high current for a brief instant (engine starting), then get immediately recharged by the alternator. Deep cycling them — draining them down over hours — permanently damages the plates within weeks. Always use a deep-cycle battery rated for house use.

How long does a LiFePO4 battery last?

Quality LiFePO4 batteries (Grade A cells, quality BMS) are rated for 3,000–5,000 cycles to 80% capacity. At one full cycle per day, that's 8–14 years. Most van batteries don't see full daily cycles — they'll last longer in practice. Premium brands like Battle Born warrant 10 years; budget brands typically warrant 3–5 years.

Can I mix different LiFePO4 brands in parallel?

No. Only parallel identical batteries — same manufacturer, same model, same capacity, and ideally the same production run. Mixing different batteries (even same brand, different model year) creates voltage imbalances during charging that can cause large equalisation currents and damage both batteries.

What happens when the BMS trips?

The battery disconnects its output — everything in the van goes off. To reset, apply a charging voltage (plug into shore power, start the engine with DC-DC charger active, or ensure solar is producing on a sunny day). The BMS auto-reconnects once it detects a valid charge source. If it trips immediately again, something is wrong — check the troubleshooting section.

Do I need a self-heating battery for winter van life?

If you camp in temperatures below 32°F and rely on solar charging, yes. Solar charges your battery even on cold mornings — without temperature protection, this means charging LiFePO4 below 32°F, which causes lithium plating. The Battle Born Heated series, or a Victron/Renogy Smart battery paired with a temperature-sensing MPPT controller, are the two approaches. If your BMS already has a 32°F charge cutoff (verify in the spec sheet), you're covered without a heater.