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The formula is dead simple: usable energy divided by daily consumption. A 200Ah LiFePO4 at 12V gives you 1,920Wh usable (at 80% depth of discharge). If you burn through 640Wh per day — fridge, lights, phones, laptop — that's exactly 3 days off-grid. Add solar and the math changes completely.
Here are the real numbers by lifestyle: weekend minimalist (lights + phone) uses 150-200Wh/day — a 100Ah LiFePO4 lasts 4-5 days. Standard vanlife (fridge + lights + laptop) burns 500-700Wh/day — 200Ah gives you 2-3 days. Digital nomad (all-day laptop + monitor + router + fridge) eats 1,000-1,400Wh/day — you need 300-400Ah for 2-3 days of buffer.
⚡ Expert tip
Don't size your battery for exactly the autonomy you need — build in a 30-40% buffer. A 3-day target means sizing for 4 days of capacity. The unexpected always happens: cloudy stretch, a night colder than forecast, the fridge running harder because you parked in the sun. Running a LiFePO4 below 20% regularly also shortens its cycle life.
Example calculation for your setup
Results based on a typical use case
| Appliance | Power | Usage/day | Wh/day |
|---|---|---|---|
| Compression fridge | 45W | 24h | 1080 |
| LED lighting | 20W | 4h | 80 |
| Water pump | 30W | 0.5h | 15 |
| Phone charging | 15W | 2h | 30 |
| Daily consumption | 1205 Wh | ||
Recommended LiFePO4 battery
126 Ah
(80% depth of discharge)
Recommended AGM battery
201 Ah
(50% depth of discharge)
Adjust these values with the calculator below
VANPOWERCALC PROYOUR ENERGY PROFILE
YOUR ENERGY PROFILE.
This document contains the sizing of your future electrical installation, calculated based on your appliances.
Minimum Daily Consumption
0 WH / DAY
Inventory:
SYSTEM SIZINGPage 2
Battery
To guarantee 0WH without damaging your bank (80% max discharge):
0 AH
LiFePO4 12V
Solar
Minimum power required to recharge your consumption:
0 W
via MPPT
220V AC
Maximum power (with 25% safety margin).
0 W
No Need
Safety & CablingPage 3
12V Cable Sizing Guide
Use this professional reference table to select the correct gauge (mm²) for your cables. For 12V in a van, the maximum tolerated voltage drop is 3%. Always use multi-stranded flexible automotive wire.
| Current (A) | Round trip < 2m | Round trip 4m | Round trip 6m |
|---|---|---|---|
| 5A (LEDs, USB) | 1.5 mm² | 2.5 mm² | 4 mm² |
| 10A (Fridge, Pump) | 2.5 mm² | 4 mm² | 6 mm² |
| 20A (Heater) | 4 mm² | 10 mm² | 10 mm² |
| 50A (DC/DC Booster) | 10 mm² | 16 mm² | 25 mm² |
| 100A (Inverter) | 25 mm² | 35 mm² | 50 mm² |
Fuse Sizing
The fuse protects the wire, not the appliance. Always place it as close to the power source as possible (battery or busbar).
- Wire 1.5 mm² → Max fuse 10A
- Wire 2.5 mm² → Max fuse 20A
- Wire 4 mm² → Max fuse 30A
- Wire 6 mm² → Max fuse 40A
- Wire 10 mm² → Max fuse 60A
SCHÉMA ÉLECTRIQUE
PANNEAUX SOLAIRES
0W
REGULATEUR MPPT
BATTERIE AUXILIAIRE
0 Ah
Lithium LiFePO4
FUSIBLE
FUSIBLE
BOÎTE À FUSIBLES 12V
Pompe, Leds, Frigo...
CONVERTISSEUR 220V
NON REQUI
PRO GEARPage 4
SHOPPING LIST
Where to find this equipment? Here is the community-approved selection.
12V 6-way Fuse Box
Mandatory protection
Digital Multimeter
Test your connections
Heavy Duty Crimping Tool
For perfect lugs
Heat Shrink Tubing
Insulation and safety
GENERATED BY VANPOWERCALC PRO - UNLIMITED.
About this tool
People always ask me how much solar changes the equation. In summer with 200W of panels, you generate roughly 800-1,000Wh per day in the southern US or Mediterranean — that covers a standard vanlife setup entirely. Autonomy becomes theoretically unlimited. But winter tells a different story. In northern states or northern Europe in January, those same 200W panels produce maybe 250-350Wh. You're running a deficit every day. That's when a DC-DC charger earns its keep — 1 hour of driving with a 30A charger produces 360Wh. Between solar and driving, most people can stretch a 200Ah bank indefinitely even in winter, as long as they drive every 2-3 days. One more thing people overlook: temperature. At -10°C, a LiFePO4 delivers only 70-75% of its rated capacity. That 200Ah battery is effectively 150Ah in a cold snap. Budget 25-30% extra capacity if you plan to winter camp.
Frequently asked questions
How do I calculate my van battery autonomy?▼
Autonomy (days) = Usable energy (Wh) / Daily consumption (Wh). For LiFePO4: Usable Wh = Ah x 12V x 0.8 (depth of discharge). So 200Ah x 12 x 0.8 = 1,920Wh. At 640Wh/day consumption: 1,920 / 640 = 3 days.
What battery size for 3 days off-grid?▼
Depends on your consumption. For standard vanlife at 600Wh/day: 600 x 3 days / 0.8 DoD / 12V = 188Ah. A 200Ah LiFePO4 is the sweet spot. For digital nomad at 1,200Wh/day: you'd need 375Ah — go with 400Ah or accept 2 days of autonomy with 200Ah.
Does cold weather reduce my battery autonomy?▼
Yes, significantly. At -10°C, LiFePO4 cells deliver about 70-75% of rated capacity. Your 200Ah battery effectively becomes 150Ah. AGM is even worse — losing up to 40% at freezing temps. In winter, oversize your battery by 25-30%.
Can solar panels make my van autonomy unlimited?▼
In summer, basically yes. 200W of solar in a sunny climate produces 800-1,000Wh/day — enough for a standard vanlife setup. In winter or overcast conditions, solar barely covers 30-50% of your needs. You'll still need to drive (DC-DC charger) or plug in (shore power) every few days.
How does a DC-DC charger affect my autonomy?▼
A 30A DC-DC charger at 12V produces 360Wh per hour of driving. One hour of driving per day adds 360Wh to your budget — that's huge. Combined with even modest solar, it's often enough to never deplete your battery. This is why I consider a DC-DC charger non-negotiable for any serious van build.