Tools · 01
Battery Bank Calculator
"How much battery do I need?" has one honest answer: add up your loads. This tool does the arithmetic the forum threads skip — appliance by appliance, with chemistry-aware usable capacity and a buffer for cloudy days. Defaults are labeled EST (spec-sheet estimate) or FIELD (observed on our own van). As bench tests publish, they become MEASURED. Every number is editable — trust your own meter over our defaults.
1 · Your daily loads
2 · Your system
"Days of autonomy" = how long the bank carries these loads with no meaningful recharge.
What this calculator assumes (and what it doesn't know)
- Nominal voltage 12.8V (LiFePO4). Ah figures scale accordingly; Wh figures don't care.
- Usable capacity: LiFePO4 sized to 80% depth of discharge for cycle life and cold-weather margin (100% selectable), lead-acid/AGM to 50%. Discharging lead-acid past half is how banks die young.
- Inverter loss: AC appliance defaults are padded ~15%. If you run everything DC, your real numbers are slightly better.
- Defaults are estimates, editable, and labeled. The fridge number is the single biggest guess in every van power budget on the internet — forum claims span nearly 10x. Our watt-hour-logger fridge test is on the bench specifically to replace that guess with a measurement.
- What it doesn't know: your ambient temperature, your insulation, your compressor's mood. Treat the output as a well-reasoned starting point, then verify with a battery monitor.
Questions people actually search
How many amp hours do I need for van life?
Most weekend builds without air conditioning land between 100Ah and 200Ah of LiFePO4 at 12V. Full-time builds with Starlink and a laptop workload typically need 200–400Ah, and any build trying to run 12V air conditioning off-grid should be planning 400Ah and up plus a serious recharge story. The honest answer is arithmetic, not a rule of thumb: add up watt-hours per day, multiply by your days of autonomy, and divide by the usable fraction of your battery chemistry — which is exactly what this calculator does.
How much power does a 12V fridge actually use per day?
Forum answers famously range from 8.8Ah to 80Ah per day, which is why we default to a middle estimate of about 325Wh (≈25Ah at 12.8V) and label it as an estimate. Real draw depends on ambient temperature, contents, and duty cycle. We have three fridges on the bench with a watt-hour logger right now; this default gets replaced with measured numbers when that test publishes.
Should I size a LiFePO4 battery to 80% or 100% depth of discharge?
LiFePO4 can technically be discharged to 100%, but sizing to about 80% usable protects cycle life, leaves margin for cold weather and battery-monitor drift, and means a cloudy extra day does not take you to zero. Lead-acid and AGM should only be sized to 50% usable. This calculator applies those fractions for you.
Do I need extra battery capacity for cloudy days?
Yes, if solar is your main recharge source. "Days of autonomy" is how many days the bank can carry your loads with no meaningful recharge. 1.5–2 days is a sane default for solar-primary builds; 1 day is fine if you drive daily and charge from the alternator.