- Work in Wh per day, not Ah alone — Ah without voltage tells you very little.
- Usable energy is about 80% of nominal capacity at 80% DOD.
- A 2,000W inverter at 12V pulls about 170A; a single 100Ah pack is rated 100A continuous.
- Check the bay and the weight before choosing the 314Ah pack.
1. Start with a load audit
List what actually runs, how many watts it draws and how many hours per day. Use the appliance label or a clamp meter; do not guess from marketing numbers.
| Load | Typical draw | Daily hours | Wh/day |
|---|---|---|---|
| 12V compressor fridge | 25–45W average | 24 (cycling) | 600–1,080 |
| LED lights | 10–20W | 4–6 | 40–120 |
| Water pump | 60–100W | 0.5–1 | 30–100 |
| Laptop / router | 50–80W | 4–8 | 200–640 |
| Inverter loads (coffee, induction) | 1,000–2,000W | 0.2–0.5 | 200–1,000 |
Add the column. A weekend van usually lands at 0.8–1.5 kWh/day; a full-time van with an induction cooktop and Starlink often needs 2–4 kWh/day.
2. Choose days of autonomy
One day is enough if you drive or plug in daily. Two to three days covers boondocking, cloudy weather and a margin for ageing. More autonomy means more weight and space.
3. Turn Wh into Ah
Use 80% depth of discharge and about 85% inverter efficiency. The formula is: daily Wh × days ÷ (0.8 × 0.85) ÷ system voltage = required Ah.
Example: 1,200 Wh/day, 2 days, 12V. 1,200 × 2 ÷ 0.68 = 3,529 Wh; ÷ 12.8V = 276Ah. One 12V 314Ah (4,019 Wh) covers it with a little headroom.
For a 2,500 Wh/day full-time van with 2 days: 2,500 × 2 ÷ 0.68 = 7,353 Wh, or about 574Ah at 12.8V. That is two 12V 314Ah in parallel (8,038 Wh), or a 24V system with two 24V 200Ah in parallel.
4. Check the inverter current
A 2,000W inverter at 12V draws about 170A at full load. The 12V 100Ah pack is rated 100A continuous; the 314Ah is rated 200A. For a 2,000W+ inverter, choose the 314Ah or a 24V system, and size cables and fuses for the surge.
Motors and compressors can draw two to three times their running current at startup. The inverter’s peak rating and the BMS surge rating both matter; the battery’s continuous rating is not the whole story.
5. Measure the bay and the weight
| Model | Dimensions | Weight | Best for |
|---|---|---|---|
| 12V 100Ah | 260 × 168 × 214.7 mm | 10.3 kg | Weekend van, 12V fridge, lights |
| 12V 314Ah | 383 × 193 × 250 mm | 26.5 kg | Full-time van, long runtime |
| 24V 100Ah | 531 × 206 × 217 mm | 18.7 kg | Native 24V, smaller current |
| 24V 200Ah | On request | On request | Large 24V bank, home backup |
Measure the door or hatch opening, not just the bay. The 314Ah is a two-person lift for most installations; plan the cable route and the fuse location before it goes in.
6. Plan the charge source
Alternator charging needs a LiFePO4-compatible DC-DC charger; solar needs an MPPT controller with a lithium profile. Neither should rely on the BMS to limit charge current.
Charging stops below 0°C on these models. If you ski or live in a cold climate, keep the battery in a heated space or warm it before charging; they do not have self-heating.