Can a 12V lithium battery run an RV air conditioner, and what must the inverter handle?

Direct answer: It can be done only if every part is sized for it. A rooftop air conditioner’s running power, divided by 12.8V and the inverter efficiency, often means more than 100A from a 12V battery, and the compressor start can draw much more for a moment. The battery’s continuous and peak ratings, the inverter’s continuous and surge ratings, and the cables and fuse must all cover those currents, and the battery bank must hold enough energy for the hours you want.

Battery figures. Redway’s 12V 200Ah (2.5 kWh), 12V 250Ah (3.2 kWh) and 12V 300Ah (3.84 kWh) list continuous current options of 100A, 150A or 200A, with matching peaks of 110A, 160A or 210A for 10 seconds. The current version must be chosen at order, so state it.

Worked example, with stated assumptions. Assume an air conditioner running at 1,300W and an inverter assumed 90% efficient. Battery current is about 1,300 ÷ (12.8 × 0.9) ≈ 113A, so a 100A version is too small and a 150A or 200A version is needed. A 3.84 kWh battery could supply about 3,840 × 0.9 ÷ 1,300 ≈ 2.7 hours before reserve; keeping 20% in reserve leaves just over 2 hours. Use your air conditioner’s figures.

Starting current. The compressor start can draw much more than running current for a moment. Check the air conditioner maker’s starting figure and the inverter’s surge rating and duration. A soft-start device, if the air conditioner maker approves it, can lower the start peak. If the start current exceeds the battery’s 10-second peak rating, the BMS may cut off; see why a 12V battery shuts off when an inverter starts.

Cable and fuse. At 110–200A on 12V, cable runs must be short and heavy, with a fuse close to the battery sized for the cable. Our post on cable and fuse for a 2,000W inverter shows the method.

Consider 24V or 48V. Higher system voltage halves or quarters the current for the same power, which eases cable, fuse and inverter sizing. For many air-conditioning setups that is the more practical route; see two 12V in series vs one 24V.