A flat battery at camp is rarely caused by one bad component. More often, the battery bank was too small, solar production was overestimated, or a high-draw appliance was added without allowing for it. This off-grid power system guide is designed for caravan owners, motorhome travellers, campers and 4WD users who want a dependable 12V setup suited to Australian travel conditions.
The right system is not necessarily the biggest system. It is the system that matches how you travel: how long you stay off-grid, where you camp, what you need to run, and whether you can drive often enough to recharge. A weekend away with a compressor fridge has very different requirements from weeks in the Kimberley with satellite TV, mobile internet, laptops and a coffee machine.
Start with your daily power use
Battery capacity and solar panel wattage should be based on consumption, not guesswork. The useful unit is watt-hours (Wh), calculated by multiplying watts by hours of use. At 12V, you can then convert watt-hours to amp-hours (Ah) by dividing by 12. In practice, allow for charging losses and voltage variation, so treat this as a planning figure rather than an exact result.
For example, a 50W compressor fridge that averages 40 per cent run time over 24 hours uses about 480Wh per day. A 12V television, VAST receiver, lights, water pump, fans, phone charging and a mobile router can easily add another 400Wh to 800Wh. That puts a modest touring setup around 900Wh to 1,300Wh a day, or roughly 75Ah to 110Ah at 12V.
Some loads change the calculation quickly. An inverter powering a toaster, hair dryer, induction cooktop or coffee machine can draw a large amount of energy in a short period. A 1,500W appliance may pull well over 120A from a 12V battery once inverter losses are included. That does not mean it cannot be used, but it needs a properly sized lithium battery, inverter, cable and fuse arrangement.
When estimating your daily load, include the equipment you use after dark and during poor weather. Refrigeration, lighting, water pumps, CPAP machines, TV and satellite equipment are often the non-negotiables. Air conditioning is in a different category altogether. Running a caravan air conditioner from batteries is possible with a substantial system, but it is not a normal small-solar application.
Choose a battery bank with usable reserve
Lithium iron phosphate, often called LiFePO4, has become the preferred battery chemistry for many caravan and off-grid systems. It offers more usable capacity, faster charging and less weight than traditional AGM batteries. A 100Ah lithium battery commonly provides close to 100Ah of usable capacity, while an AGM battery should generally not be regularly discharged as deeply if you want reasonable service life.
Battery sizing comes down to autonomy: how many days you want to operate without meaningful charging. If your estimated use is 100Ah per day, a 200Ah lithium bank provides roughly two days of usable power under favourable conditions. It is a sensible starting point for many travellers, but it may be inadequate if you rely on an inverter, have limited solar roof space, camp in shade or spend long periods stationary.
A larger battery bank gives breathing room, but only if you have a realistic way to recharge it. A 400Ah battery bank that receives little solar and only a short drive every few days will still end up flat. Consider battery capacity and charging sources as one package.
Check battery discharge and charging limits
Not all lithium batteries are identical. Check the continuous discharge rating, peak discharge rating, low-temperature charging protection and recommended charge current. These details matter when selecting an inverter and DC-DC charger. A battery with a 100A continuous discharge limit is not suitable for continuously supporting a heavily loaded 2,000W inverter, even if the battery capacity appears adequate.
Size solar for real Australian conditions
Solar output on a clean, clear summer day can be excellent. It drops sharply with cloud, shade, winter sun angles, heat and poor panel orientation. Caravan roof panels are usually flat, which is convenient but not always ideal for production.
As a broad planning approach, 400W of fixed solar may produce enough energy to cover a typical 100Ah daily load in good conditions. It may not do so every day, particularly in winter or under trees. If you regularly free camp, extra panel capacity is usually more useful than running solar at its absolute limit.
Fixed roof solar is simple and charges whenever the vehicle is parked in the sun. Portable panels can be moved into better light while the caravan stays in shade, making them useful for bush camps. Their trade-off is setup time, storage space and the need to secure them from wind, damage or opportunistic theft.
An MPPT solar regulator is generally the right choice where panel voltage and battery voltage differ, or where you want to get better use from available solar input. Select a regulator that can safely handle the panel array's maximum open-circuit voltage and current, not just its advertised wattage. Allowing for expansion at the design stage can avoid replacing the regulator later.
Do not rely on solar alone
A well-designed off-grid system normally has more than one charging source. Solar handles the daily load when conditions are good. A DC-DC charger replenishes the battery while towing or driving. Mains charging restores the bank when you stay in a powered site or return home.
A DC-DC charger is particularly important in modern vehicles with smart alternators and long cable runs to a caravan battery. It provides the correct charge profile and helps prevent voltage drop from reducing charge performance. The charger must be sized for the vehicle, cable run, battery specification and available alternator capacity. Bigger is not automatically better if the wiring cannot support it safely.
For many touring caravans, a practical combination is fixed solar, a quality MPPT regulator, a DC-DC charger and a 240V mains charger. This gives you options when rain, shade or short driving days limit any one source.
Build the system around safe cabling and protection
Good batteries and solar panels cannot compensate for undersized cable or missing circuit protection. At 12V, even a small voltage drop can affect fridge performance, inverter operation and charging efficiency. High-current loads need appropriately sized cable for both current and cable length.
Every positive cable connected to a battery should be fused or protected as close to the battery as practical. Fuses protect the cable, not the appliance, so their rating must suit the cable size and expected load. Inverters, DC-DC chargers, solar regulators and distribution circuits each need suitable protection and isolation.
Use proper crimp terminals, secure cable routing and abrasion protection where wiring passes through metal or near moving parts. Keep battery connections tight and accessible for inspection. In caravans and 4WDs, vibration and corrugated roads expose poor workmanship quickly.
A battery monitor with a shunt is one of the most useful additions to an off-grid system. Voltage alone is not a reliable indication of lithium battery state of charge. A monitor shows current flow, energy used and remaining capacity, helping you make decisions before the battery management system disconnects the load.
Inverters need careful matching
Choose a pure sine wave inverter for sensitive electronics, chargers, televisions and most household appliances. Size it according to the appliances you genuinely plan to run, including startup surge. Also account for idle consumption. Leaving a large inverter on all day can waste meaningful power when it is only supplying a small charger or standby load.
It is often better to run 12V equipment directly where possible. A 12V TV, compressor fridge, USB charging outlet and 12V satellite receiver avoid conversion losses. For caravan entertainment, check the power draw of the television, receiver, dish controller and any mobile internet equipment together, rather than sizing around the TV alone.
Plan for how and where you travel
The best design changes with the destination. A traveller moving every day can make strong use of DC-DC charging. Someone staying in one remote camp for a week needs greater solar capacity, battery reserve or a backup generator. A shaded coastal site may favour portable solar, while a dusty inland trip calls for regular panel cleaning and secure external connections.
Also consider installation space and weight. Lithium saves weight compared with AGM, but panels, brackets, cable, chargers and inverters all add up. Roof space may be constrained by hatches, air conditioners, satellite dishes and vents. A system plan should account for service access, ventilation requirements and future upgrades before drilling holes or ordering parts.
If you are unsure about compatibility, get the whole layout checked before purchase. Access 2 QLD Antennas and Satellites can help match caravan-ready batteries, solar charging equipment, inverters and accessories to the way you travel, rather than leaving you to piece together a system from mismatched ratings.
A practical off-grid power system guide checklist
Before settling on equipment, confirm four things: your estimated daily energy use, the number of battery-only days you need, the charging available from solar and driving, and the largest load the system must safely support. Then check cable lengths, fuse ratings, physical mounting positions and whether each component has room for expansion.
Electrical work on 240V circuits and any installation that falls outside your competence should be completed by a suitably qualified person. A tidy, protected 12V system is not just more reliable on the road. It is easier to diagnose when something does go wrong.
The most satisfying off-grid setup is the one you stop thinking about: the fridge stays cold, the lights work, the battery monitor remains comfortably in range, and you can stay an extra night because your power system was planned for the real trip.