Van Battery Sizing

Why Is Battery Sizing the Most Important Electrical Decision?

Your battery bank is the foundation of your electrical system. It's where all your power lives, and sizing it wrong is one of the most common mistakes we see. Too small and you're dead in the water on day two. Too big and you've spent money you didn't need to spend.

The good news is that sizing a battery is straightforward math. It takes 20 minutes to figure out how much capacity you actually need.

How Do You Calculate Your Daily Power Draw?

Start with the basics: how much power do you actually use in a day? Make a list of everything that runs on your battery and estimate how long it runs each day.

Common Power Draw Examples

Fridge (12V compressor): 20-30A per hour, runs 8-12 hours per day depending on heat and how often it cycles. On average, 150-200Ah per day. This is your biggest draw.

Lights (LED): 0.5-1A per bulb, typical van has 5-10 lights. If you run lights 4 hours per evening, that's 10-30Ah per day.

Water pump: 2-3A per minute, used maybe 30 minutes per day for showers and washing. About 60-90Ah per day.

Furnace or heating: 5-10A, runs 6-8 hours on a cold night. 50-80Ah per day in winter. Skip this in summer.

Laptop/phone charging: 5-10A per device, maybe 2-3 hours per day. 10-30Ah per day.

TV/entertainment: 3-5A, maybe 2-3 hours per day. 10-15Ah per day.

Microwave or toaster: High draw, usually runs off an inverter (AC power), not 12V battery. If you run a microwave for 15 minutes, that's 50-100Ah from the battery depending on your inverter efficiency.

Example: Weekend Van

Fridge (150Ah) + lights (20Ah) + water pump (60Ah) + laptop (15Ah) + evening entertainment (15Ah) = 260Ah per day in ideal conditions.

That's a moderate draw. You'd want at least 150-200Ah of usable capacity to get 2-3 days between charges without dropping below 50%.

Example: Full-Time Off-Grid

Fridge (150Ah) + lights (30Ah) + water pump (60Ah) + furnace (70Ah winter) + laptops/work (30Ah) + microwave (100Ah for cooking) + backup = 450Ah per day on a winter day with cooking and heating.

This needs 300-400Ah of usable capacity to go 1-2 days between charges and stay above 20% (safe minimum).

How Often Will You Recharge Your Van Battery?

How often do you want to recharge? That determines capacity.

Weekend trips: You might camp 2 nights before heading home to shore power. That's 2 days of draw. Or you plug into a campground on night 2. A smaller battery (100-150Ah) is fine because you're not going long without charging.

Extended boondocking: You want to stay off-grid for a week between charges. Now you need 4-7 days of capacity, which is much larger (200-300Ah+). Plus you need solar to recharge.

Full-time with mixed usage: You spend 3 days boondocking, then a few days at campgrounds. You need enough capacity for 3-4 days plus solar to top off. 200-300Ah is typical.

How Much of Your Battery Capacity Is Actually Usable?

This is critical. You can't use all of your battery capacity. Going below 20% on any battery damages it long-term. Lithium can go to 5-10% safely, but it's not recommended. We always design systems where you never drop below 20%.

Lithium Batteries

Lithium (LiFePO4) can safely discharge to 80-90% of capacity. If you have a 100Ah lithium battery, you get 80-90Ah of usable power. We use batteries from brands like Battle Born, Victron, and Epoch — all have built-in BMS (battery management system) and proven track records in van builds. Some high-end lithium packs let you go to 95%, but we design for 80% to extend lifespan.

On a 100Ah lithium, you're working with 80Ah usable capacity. On a 200Ah, you get 160Ah. On a 300Ah, you get 240Ah.

AGM Batteries

AGM batteries can only discharge to 50% without damage. A 100Ah AGM gives you 50Ah usable. A 200Ah AGM gives you 100Ah usable. This is why people say "buy twice as much AGM capacity as lithium" — you're literally only using half.

For a 100Ah usable draw, you'd need a 200Ah AGM battery. Same draw needs a 125Ah lithium battery. Lithium wins on space and weight.

What Are the Most Common Van Battery Configurations?

100Ah Lithium Battery

Usable capacity: 80Ah

Best for: Weekend trips, low power draw, vehicles with good alternator charging. You camp 2 nights and head to shore power or rely on your engine alternator to charge during driving.

Daily draw limit: 40Ah per day if you want to go 2 days between charges. A fridge and lights only, no water heating or heating.

Pros: Smallest, lightest, cheapest lithium option. Fits under seats or tight spaces.

Cons: Not much margin for error or adding appliances later. Most people outgrow this fast.

200Ah Lithium Battery

Usable capacity: 160Ah

Best for: Extended weekend trips, moderate full-time use, boondocking 3-5 days between charges. This is our most common configuration.

Daily draw limit: 80Ah per day and stay above 20%. A fridge, lights, water pump, heating, and some cooking. You're comfortable for a week-long trip if you have solar.

Pros: Huge sweet spot. Gives you real power without being massive. Affordable upgrade from 100Ah.

Cons: Takes up some floor or cabinet space. Heavier (150-200 lbs). Overkill if you're only weekend camping at hookups.

300Ah+ Lithium Batteries

Usable capacity: 240Ah+ (at 80%)

Best for: Full-time off-grid living, remote travel, winter camping with heating, digital nomads. You can stay boondocked 7-10 days with moderate draw.

Daily draw limit: 120Ah per day and still stay safe. Everything in the van — fridge, water heater, heating, cooking, entertainment — all day, every day.

Pros: Freedom. You can run anything without thinking about battery level. Solar tops you off, alternator does the rest. True off-grid living.

Cons: Expensive ($8K-15K+). Requires floor space or a custom setup. Heavier (400+ lbs). Need quality solar and a good charge controller to recharge it.

Should You Choose Lithium or AGM Batteries for a Van?

Lithium (LiFePO4)

Pros: 80%+ usable capacity, lighter, smaller, faster charging, 5,000+ cycle lifespan (10+ years), no maintenance. You get more usable power in a smaller package.

Cons: Expensive upfront ($3-5 per watt vs. $0.50-1 for AGM). Need a quality battery management system (BMS) for safety.

Best for: Most van builds. The extra cost is worth it for space, weight, and reliability. Even on a budget build, lithium often makes sense.

AGM (Absorbent Glass Mat)

Pros: Cheap upfront, rugged, can take abuse, no BMS required, works in cold better than lithium.

Cons: Only 50% usable capacity, heavy, takes longer to charge, 500-1,000 cycle lifespan (2-5 years), needs maintenance (cleaning terminals, checking water on wet cells).

Best for: Tight budgets or backup systems. If cost is the main constraint and you don't mind the weight, AGM works.

What Are the Most Common Battery Sizing Mistakes?

Undersizing to Save Money

This is the biggest mistake. Someone buys a 100Ah battery thinking it'll be "enough," then takes a trip and hits zero power at 2pm. Undersizing costs more in the long run because you'll upgrade later or regret it every trip. Buy bigger than you think you need.

Oversizing Without a Plan

The opposite problem: buying 400Ah of battery when you only need 200Ah because you want to "be safe." That's expensive dead weight. Size it for your actual use, not your fantasy scenario.

Forgetting About Solar

A big battery is only useful if you can recharge it. Without enough solar, your 300Ah battery stays half-full. Make sure your solar capacity matches your battery. A good rule: 1W of solar per 2-3 amps of daily draw.

Not Accounting for Winter

Winter heating draws a lot of power and solar production drops. If you're living full-time in a cold climate, size for winter, not summer.

How Much Do Van Batteries Cost by Build Tier?

These are for quality lithium batteries with integrated BMS. Cheap knockoff lithium or used batteries are cheaper but less reliable. AGM costs about 40% less but remember you're getting half the usable capacity.

Where Should You Mount and Wire Your Van Battery?

Your battery goes somewhere safe: under a seat, in a cabinet, or in a dedicated battery box. Wherever it goes, it needs ventilation (if AGM), secure mounting to prevent shifting, and clear routing of power cables.

All battery-to-distribution wiring must be properly sized for the current (we use marine-grade cable), fused at the battery terminals, and routed away from hot surfaces or moving parts. Bad wiring is dangerous and wastes power.