VANPOWERCALC

Sizing Your Camper Van Battery Bank: A Power Audit Guide

Step-by-step power audit to accurately size your camper van battery bank based on your own power consumption, not guesswork.

The Power Audit: Your #1 Tool

Every camper van battery question starts and ends with one thing: how much power do YOU actually use? Not what a blog tells you, not what your neighbor's van uses — your actual daily consumption in watt-hours. Without this number, you're guessing with hundreds of dollars on the line.

Step 1: List Every Device

Create a spreadsheet with four columns: Device, Watts, Hours/Day, and Wh/Day. Here's a realistic example for a full-time van dweller:

  • Compressor fridge (Dometic CFX 45): 45W × 10h = 450 Wh
  • MaxxAir fan: 30W × 8h = 240 Wh
  • Diesel heater fan: 25W × 6h = 150 Wh
  • LED lighting: 20W × 4h = 80 Wh
  • Water pump: 60W × 0.3h = 18 Wh
  • Phone/laptop charging: 100 Wh (flat)
  • Starlink Mini: 30W × 8h = 240 Wh
  • Total: ~1,278 Wh/day

Step 2: Convert to Battery Capacity

Divide total Wh by your battery's nominal voltage: 1,278 ÷ 12.8V = 100 Ah per day. For 2 days of autonomy without any charging: 100 × 2 = 200 Ah. With LiFePO4 (95% usable depth of discharge), a 200Ah battery gives you exactly that. With AGM (50% usable), you'd need 400Ah — twice the weight and cost.

One Battery or Multiple?

For most van builds, a single high-capacity LiFePO4 battery (200-300Ah) is simpler and more reliable than paralleling multiple smaller ones. Parallel batteries must be identical in brand, capacity, age, and state of health — if one battery is slightly weaker, it becomes a parasitic load on the others, causing premature BMS shutdowns. If you absolutely need more than 300Ah, use two identical batteries from the same production batch with matched internal resistance.

⚡ Expert tip
Counter-intuitive: for seasonal van lifers (spring-autumn), AGM batteries are often more cost-effective than LiFePO4. If you do only 200 cycles/year maximum, a quality AGM (800 cycle rated) lasts 4 years vs LiFePO4's 15-20 — but costs 3× less upfront. LiFePO4 only wins economically when you exceed 300+ cycles per year (full-time van life).

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Comparison table

Van SetupDaily Use (Wh)Battery (LiFePO4)Battery (AGM equiv.)
Weekend warrior400-600 Wh100Ah200Ah
Part-time vanlife700-900 Wh200Ah400Ah
Full-time + Starlink1000-1300 Wh300Ah600Ah
Digital nomad + AC1500-2000 Wh400Ah+Not practical

About this tool

Determining how many batteries you need for a DIY campervan build comes down to answering three questions in sequence: how much energy do you use per day, how many days should you run without recharging, and what chemistry are you using?

Step 1: Real daily consumption. The most common mistake is underestimating — especially the refrigerator and laptop. A 12V compressor fridge (most recommended for vans) cycles on and off throughout the day. At 22°C ambient, it might run 40% of the time at 50W = 480Wh/day. At 30°C summer ambient with frequent opening, that easily becomes 600-700Wh/day. Add: laptop 7 hours (70W × 7 = 490Wh), LED lights evening (25W × 4h = 100Wh), phone and accessories (50Wh), water pump (15Wh), diesel heater (100Wh in winter). Total: 1255Wh/day for a comfortable full-time setup.

Step 2: Autonomy days. For a van with 300W solar in France (4h PSH × 0.8 efficiency = 960Wh/day production), deficit vs consumption = 295Wh/day. On a cloudy travel day with no sun: full 1255Wh comes from battery. Two cloudy days = 2510Wh from battery with no recharge. Plan for 2-3 days of zero-solar autonomy.

Step 3: Battery size. For 2.5 days at 1255Wh/day: 3137Wh stored needed. LiFePO4 at 100% DOD usable: 3137Wh ÷ 12V = 261Ah. Choose 300Ah (provides 10% headroom and accounts for minor capacity degradation over years). Options: one 300Ah unit (€700-900) or two 150Ah in parallel (€400-600).

Parallel battery banks — making the right choice: two batteries in parallel should ideally be identical (same manufacturer, capacity, and ideally same batch) to ensure balanced charge sharing. Mismatched batteries in parallel have different internal resistances — the lower-resistance battery receives more charge/discharge current, degrading faster. If adding a second battery to an existing system, match manufacturer recommendations closely.

The 12V vs 24V decision for battery banks: most DIY van builds use 12V because it simplifies the appliance ecosystem (12V compressor fridge, 12V fans, 12V LED circuits). 24V makes sense when inverter loads are large (3000W+ true off-grid setups) since halved current = halved wire size requirements. Hybrid: use 12V for house loads and 24V nominal batteries with a 24V-to-12V DC-DC for 12V appliances.

BMS (Battery Management System) compatibility when paralleling: each battery must have its own BMS unless you're building from raw cells. Two batteries with internal BMS in parallel can create current races during reconnection — the higher-charge battery pushes current into the lower one, potentially causing one BMS to trip on overcurrent. Best practice: charge both to identical voltage before connecting in parallel, or use a Victron Lynx Shunt + Distributor for managed parallel connections.

Frequently asked questions

How many batteries for a 200W solar panel van?▼
It depends on consumption. 200W at 4 PSH = 640Wh production. If you consume 600Wh/day, you need storage for 1-2 buffer days = 600-1200Wh → 50-100Ah LiFePO4 minimum. Practical recommendation: 100Ah LiFePO4 (€250) for basic van life + 200W solar.
What is the difference between 100Ah AGM and 100Ah LiFePO4?▼
100Ah AGM: 600Wh usable (50% maximum DOD). 100Ah LiFePO4: 1200Wh usable (100% DOD). Same physical size, 2× usable energy, 10× the cycle life. AGM: €120-150. LiFePO4: €250-350. For any system used more than 100 times per year, LiFePO4 is economically superior long-term.
Can I wire two different LiFePO4 batteries in parallel?▼
Technically yes, but not recommended. Different internal resistances cause unequal current sharing — the lower-resistance battery gets stressed more. If necessary, charge both to identical voltage before connecting. Ideally: same brand, same model, same capacity.
How many amp hours for full-time van life?▼
Typical full-time van life consumption: 800-1500Wh/day depending on equipment. For 2 days autonomy with LiFePO4: 100-250Ah. Most full-timers with solar run 200Ah LiFePO4 + 300W solar — comfortable in spring/fall, may need driving charging in winter.
Should I buy 12V or 24V batteries for a van?▼
12V for most van builds — simplifies the appliance ecosystem (12V fridge, fans, lighting work directly). 24V if planning 3000W+ inverter setups or long cable runs (lower current in cables). Most DIY van builders choose 12V and never need to upgrade.

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