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

· 4 min read

Your house battery (also called the auxiliary or "coach" battery) is the heart of a van or RV electrical system. Size it right and you'll have worry-free power for years; size it wrong and you'll be hunting for a generator on night two. This guide covers battery types, watt-hour sizing, wiring, and US product picks.

For how the battery fits into the bigger picture, see the complete electrical system guide.

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LiFePO4 vs. AGM

For US van builds in 2026, there are two practical choices.

LiFePO4 (lithium iron phosphate) — the standard

  • 80–100% usable capacity vs. ~50% for AGM
  • 3,000–5,000+ cycles (roughly 8–15 years of typical use)
  • Half the weight of equivalent AGM
  • Flat voltage — holds ~13V until nearly empty
  • Built-in BMS protects against over-charge, over-discharge and short circuit

Higher upfront cost, but the lowest cost-per-cycle by far.

AGM (absorbent glass mat) — budget/weekender only

  • Cheaper upfront (~$150–$220 for 100Ah)
  • Only ~50% usable (a 100Ah AGM gives you ~50Ah)
  • Heavier, and 300–500 cycles

How to size your bank (watt-hours)

The clean way to size a 12V bank:

  1. Daily energy use in Wh (add watts × hours for every appliance).
  2. Divide by usable depth of discharge: LiFePO4 ÷ 0.8, AGM ÷ 0.5.
  3. Convert to amp-hours: result ÷ 12.8.
  4. Add ~20% headroom and round up.

Example: 1,200Wh/day ÷ 0.8 = 1,500Wh ÷ 12.8 = ~117Ah, +20% ≈ 140Ah → round to 150–200Ah LiFePO4.

Planning on induction cooking or AC?

Induction cooktops pull 1,500–1,800W and rooftop air conditioners are brutal on a battery. Both push you toward 300Ah+ and a larger inverter. The inverters guide explains the trade-offs.

US battery picks (USD)

These are popular, well-supported choices — confirm current pricing before you buy.

  • Best value: LiTime 12V 100Ah ($220) or 200Ah ($399) — strong specs for the money, 100A/200A BMS.
  • Mid-range with self-heating: Renogy 12V 100Ah Smart (~$259) — Bluetooth, good support.
  • Premium, US-made: Battle Born 100Ah (~$799–$949) — internal heating, 10-year warranty, excellent reliability record.

Wiring multiple batteries

If one battery isn't enough, wire identical units in parallel (positive to positive, negative to negative) to keep 12V while adding capacity.

Never mix batteries

Don't mix chemistries (AGM + lithium) or different capacities/ages in parallel — it causes dangerous current imbalance. Use identical batteries, and take the main positive and negative from diagonally opposite corners of the bank so they share load evenly.

Each battery's main cable still needs proper AWG sizing and a high-interrupt fuse — see the wiring & safety guide.

Cold-weather charging

LiFePO4 must not be charged below 32°F (0°C) or you'll damage the cells. Most quality batteries either block charging via the BMS or include internal heating (like the Battle Born heated models). If you'll camp in freezing temps and recharge from solar, either choose a self-heating battery or keep the bank in a heated space and charge during the warmer part of the day.

Monitoring

You can't manage what you can't measure. A shunt-based monitor like the Victron SmartShunt (~$120) tracks every amp in and out and shows a true state-of-charge percentage — far more accurate than guessing from voltage.

FAQ

What size house battery do I need for a van?

For a weekender (fridge, lights, USB), 100–150Ah of LiFePO4 is usually plenty. For full-time use with a laptop and moderate loads, 200Ah is the sweet spot. For induction cooking or air conditioning, plan on 300Ah+. Use the free calculator for an exact figure.

How long does a LiFePO4 house battery last?

A quality LiFePO4 battery lasts 3,000–5,000+ charge cycles — roughly 8–15 years of typical van use. AGM lasts 300–500 cycles, or about 2–4 years.

Can I use a car battery as a house battery?

No. Starter batteries deliver high current for a few seconds, not sustained discharge over hours. Used as a house battery, one will fail within weeks. Always use a deep-cycle LiFePO4 or AGM battery.