How to Size a Lithium Battery for Off-Grid and RV Use
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Why Lithium Batteries Are the Off-Grid Standard
If you're setting up a caravan, camper trailer, or off-grid power system, lithium (LiFePO4) batteries have become the go-to choice — and for good reason. Compared to traditional AGM or lead-acid batteries, lithium batteries offer a deeper usable capacity, a longer cycle life, faster charging, and significantly less weight. But choosing the right size is critical. Too small and you'll be rationing power; too large and you've spent more than you needed to.
This guide walks you through how to calculate the right battery capacity for your setup.
Step 1: Work Out Your Daily Power Consumption
Start by listing every 12V appliance you plan to run and how long you'll use it each day. Multiply the wattage by the hours of use to get watt-hours (Wh).
Here's a typical example for a weekend camper:
- Diesel heater (running): 20W × 8 hours = 160Wh
- 12V fridge (50W average): 50W × 24 hours = 1,200Wh
- LED lighting: 10W × 4 hours = 40Wh
- Phone/device charging: 20W × 2 hours = 40Wh
- Water pump: 60W × 0.5 hours = 30Wh
Total daily consumption: ~1,470Wh
Step 2: Convert Watt-Hours to Amp-Hours
Battery capacity is measured in amp-hours (Ah) at 12V. To convert:
Ah = Wh ÷ 12
So 1,470Wh ÷ 12 = ~122Ah per day.
Step 3: Account for Usable Capacity and Autonomy
Lithium batteries can safely discharge to 80–90% of their rated capacity (unlike AGM which is typically limited to 50%). However, you should still plan for at least 1–2 days of autonomy without solar input — for cloudy days, shaded campsites, or simply not wanting to stress your system.
Using 2 days of autonomy and 90% usable depth:
Required capacity = (Daily Ah × Days of autonomy) ÷ Usable depth
= (122Ah × 2) ÷ 0.9 = ~271Ah
In this case, a 300Ah battery would be the right fit.
Our Lithium Battery Range
We stock a range of premium lithium batteries to suit different setups and budgets:
- Nomadic Premium 150Ah Lithium Battery — a solid choice for smaller setups: camper trailers, rooftop tents, or weekend getaways with modest power needs. Pairs well with a 2kW diesel heater and a small fridge.
- Nomadic Premium 230Ah Lithium Battery — the sweet spot for most caravan setups. Handles a fridge, lighting, diesel heater, and device charging comfortably for 1–2 days without solar.
- Nomadic Premium 300Ah Lithium Battery — ideal for extended off-grid trips, larger caravans, or anyone running high-draw appliances like a CPAP machine, inverter, or air compressor.
- Finch 150Ah Lithium Deep Cycle Battery — a compact, value-focused option for budget-conscious setups that still want the benefits of lithium chemistry.
- Finch 200Ah Lithium Deep Cycle Battery — steps up capacity for those who need a bit more headroom without going to a full 300Ah bank.
Quick Sizing Reference
| Setup Type | Typical Daily Use | Recommended Capacity |
|---|---|---|
| Weekend camper (basic) | Fridge + lighting + phone | 150Ah |
| Caravan (standard) | Fridge + heater + lighting + devices | 200–230Ah |
| Extended off-grid / full-timer | All of the above + inverter loads | 300Ah+ |
Do You Need More Than One Battery?
If your power needs exceed 300Ah, you can connect multiple lithium batteries in parallel to increase capacity. Most lithium batteries support parallel connection — just make sure you're using identical batteries from the same brand and ideally the same production batch for best results.
Don't Forget Your Charging Sources
A battery is only as good as your ability to recharge it. For most RV setups, you'll want a combination of:
- Solar panels — the most common off-grid charging source. As a rough guide, 100W of solar generates around 30–40Ah per day in good Australian sun.
- DC-DC charger — charges your battery from your vehicle's alternator while driving. Essential for maintaining charge on travel days.
- 240V mains charger — for when you're on a powered site or at home.
If you're running a 200Ah battery and consuming 120Ah per day, you'd want at least 200W of solar to reliably recharge in a single day.
Summary: How to Choose
- Calculate your daily Wh consumption, then divide by 12 to get daily Ah.
- Multiply by your desired days of autonomy and divide by 0.9 for usable depth.
- Round up to the nearest available battery size.
- Plan your charging sources to match your daily consumption.
Still not sure which battery suits your setup? Browse our full RV and off-grid range or reach out — we're happy to help you size your system correctly.