RV/Van Life Battery Bank Sizing Calculator
Created by: Ethan Brooks
Last updated:
Size your RV or van life battery bank based on daily energy consumption, desired days of autonomy, and battery chemistry. Compare lithium vs AGM options with cost and weight estimates.
What is an RV/Van Life Battery Bank Sizing Calculator?
An RV/Van Life Battery Bank Sizing Calculator helps you determine the right battery capacity in amp hours (Ah) for your camper van, motorhome, or RV. By entering your daily power consumption and desired days of backup power, you can calculate the optimal battery bank size for reliable off-grid living.
Whether you choose lithium (LiFePO4) or lead-acid (AGM) batteries, this calculator accounts for depth of discharge limits and real-world factors to ensure your battery bank meets your actual needs without overspending.
Understanding Battery Bank Sizing
Amp Hours (Ah): Battery capacity - how many amps can be drawn for how many hours
Depth of Discharge (DoD): How much capacity you can safely use (50% AGM, 80-100% lithium)
Days of Autonomy: How many days you want to run without charging
Basic Formula: Battery Ah = (Daily Wh ÷ Voltage) × Days ÷ DoD
Frequently Asked Questions
How many amp hours do I need for van life?
Most van lifers need 100-400Ah of lithium battery capacity. Calculate by dividing daily Wh consumption by system voltage. For 1200Wh daily use on a 12V system, you need 100Ah minimum. Add 20-50% buffer for days without solar, making 150-200Ah ideal for that usage level.
Should I get lithium or AGM batteries for my van?
Lithium (LiFePO4) batteries are superior for van life: 80-100% usable capacity vs 50% for AGM, 3000+ cycles vs 500, half the weight, and faster charging. They cost 2-3x more upfront but last 6-10x longer, making them cheaper long-term for frequent use.
What's the difference between usable and rated capacity?
Rated capacity is the battery's total Ah. Usable capacity is what you can safely use: lithium batteries provide 80-100% usable capacity, AGM/lead-acid only 50%. A 200Ah AGM gives you 100Ah usable; a 200Ah lithium gives you 160-200Ah usable.
How many days of autonomy should I plan for?
Plan for 1-3 days of autonomy (backup) depending on your travel style. Weekend campers: 1 day. Regular travelers: 2 days. Extended boondockers or cloudy climates: 3+ days. More autonomy means larger battery bank but also more weight and cost.
Can I mix different battery types or sizes?
Never mix battery chemistries (lithium with AGM). Mixing sizes of the same type is possible but not recommended—the smallest/oldest battery limits the bank. For best results, use identical batteries purchased together.
What size alternator charger do I need?
Size your DC-DC charger at 20-40 amps for most van builds. Larger isn't always better—your alternator needs headroom. A 40A charger with 4 hours of driving charges ~160Ah into your batteries, enough for most daily needs.
How do I calculate battery bank weight?
Lithium batteries weigh about 13-15 lbs per 100Ah. AGM batteries weigh about 60-70 lbs per 100Ah. A 200Ah lithium bank weighs 26-30 lbs total; the same capacity in AGM weighs 120-140 lbs. Factor weight into your cargo capacity.
What happens if I discharge batteries too deeply?
Deep discharge damages batteries and shortens lifespan. AGM batteries degraded quickly below 50% charge. Lithium batteries handle deeper discharge but still benefit from staying above 20%. Most BMS systems cut off at 0-10% to protect cells.
Sources and References
- Battle Born Batteries, "Lithium Battery Sizing Guide", 2024
- Victron Energy, "Battery Capacity and C-Rating Explained", victronenergy.com
- Will Prowse, "DIY Lithium Battery Builds", DIYSolarForum.com, 2024