1. Add up a real day
Watts × hours for every load, then add about 30% for inverter losses, cold weather and ageing. A weekend van often lands at 0.8–1.5 kWh/day; a full-time van with induction and Starlink at 2–4 kWh/day.
Size the bank around a real day of use: the fridge cycles all night, the inverter pulls a surge at breakfast, and the alternator only charges while you drive.
A 12V house bank is the simplest upgrade for most vans. The two decisions that matter are daily energy (Wh) and whether you need a 24V system for a large inverter. Capacity in Ah alone tells you very little without the voltage.
Sizing rule: daily Wh first, then autonomy, then the model.
The arithmetic is simple; the mistakes come from using running watts instead of surge, or Ah without the voltage.
Watts × hours for every load, then add about 30% for inverter losses, cold weather and ageing. A weekend van often lands at 0.8–1.5 kWh/day; a full-time van with induction and Starlink at 2–4 kWh/day.
One day is fine if you drive or have shore power daily. Two to three days of autonomy covers boondocking and cloudy weather. More autonomy means more weight and space — check the bay before you go bigger.
A 2000W inverter at 12V pulls about 170A — more than a single 100Ah pack’s 100A continuous limit. For large inverters, use the 314Ah (200A BMS) or a 24V system, and size cables and fuses for the surge.
Example: 1,200 Wh/day, 2 days of autonomy, 12V system. Required ≈ 1,200 × 2 ÷ (0.8 × 0.85) = 3,529 Wh, or about 276 Ah at 12.8V. One 12V 314Ah (4,019 Wh) covers it with a little headroom.
Assumes 80% depth of discharge and 85% inverter efficiency. Cold weather, ageing and higher inverter losses need extra margin.
Start with the smallest pack that covers the load, then check the bay and the inverter surge.
The everyday 12V pack. Light enough to swap by hand, with 100 A continuous output and 4S4P expansion.
Best for: Weekend RVs, camper vans, 12V fridges, small boat electronics.
Bank limit: 4S4P
Three times the capacity of the 100 Ah pack in one box — fewer parallel connections and a 200 A BMS.
Best for: Full-time vans, larger 12V banks, long runtime without recharging.
Bank limit: 4S4P
The largest pack we list today: 5.1 kWh in one 24V case, parallel up to 1S4P.
Best for: Home backup, larger 24V house banks, multi-day off-grid loads.
Bank limit: 1S4P
Not sure? Use the sizing calculator, or send us the load list and we will check it.
Include the application, daily runtime, inverter size and destination market. We will reply with a model recommendation and the matching datasheet.