An inverter changes battery power into 230-volt AC power. The right size is not simply the wattage of your biggest appliance: it must cover the appliances you plan to run together, their start-up surge and what the battery system can safely supply.
1. List the AC appliances you genuinely need off-grid
Use each appliance's input watts from its rating plate or manual. Chargers and televisions may be modest loads; kettles, coffee machines, induction cooking, hair dryers and air conditioners can be much larger.
2. Add simultaneous loads
Victron's official inverter selection guidance says the inverter should support the highest expected continuous demand, including appliances used at the same time. Decide which high-draw appliances will never run together rather than sizing from an unrealistic total.
3. Allow for start-up surge
Compressors, pumps and motors can draw more power when starting. Compare both continuous and peak ratings in the appliance and inverter manuals. A watt figure and a VA rating are not always interchangeable for every load.
4. Check the DC side
A 2,000 W load can demand roughly 167 A from a 12 V battery before inverter losses. Battery chemistry, BMS limits, cable length, conductor size, fusing, temperature and connection quality all matter. A large inverter on an undersized battery system is not a workable design.
Practical selection rule
Choose from your measured continuous load, verified surge requirement and an appropriate margin—not from a generic caravan size. Pure sine wave output is normally the appropriate choice for sensitive electronics, but confirm appliance requirements.
Use the Battery Capacity Calculator, Solar Requirement Calculator and Off-Grid Days Calculator to understand the broader energy system.