Can I Run AC Off Batteries

The short answer and the big variables

Running air conditioning from batteries is possible, but the details matter. The air conditioner’s watt draw, your usable battery capacity, inverter efficiency, and the duty cycle all determine how long you can stay cool. Most rooftop units draw 1000 to 1800 watts when the compressor is on, and they cycle on and off depending on heat load. Lithium iron phosphate batteries are the common choice because they deliver high discharge rates, deep usable capacity, and consistent voltage. Plan the system like a calculator problem, not a guess.

Load and duty cycle, translated

Two numbers drive the plan. First is the continuous wattage while the compressor is running. Second is the duty cycle, which is the percentage of time the compressor actually runs over an hour. A 13.5k BTU rooftop unit might average 40 to 60 percent duty cycle on a mild day but can climb near continuous in peak heat. If your unit pulls 1400 watts and averages 50 percent duty cycle, your hourly energy use is about 0.7 kWh.

Battery capacity that actually counts

Battery capacity is best compared in kilowatt hours. Convert amp hours to kWh with V times Ah divided by 1000. A 12 volt 400 Ah lithium bank is roughly 4.8 to 5.1 kWh usable when you account for inverter losses and realistic discharge. At a 0.7 kWh per hour cooling load, that bank gives about 6 to 7 hours before hitting prudent depth of discharge limits. Smaller banks shrink runtime fast. Larger banks smooth out the spikes and support multi hour comfort.

Inverters, startup surges, and soft starts

If your AC is a 120 volt unit, size the inverter for both running watts and the compressor surge. Many modern air conditioners paired with a soft start reduce the surge dramatically. A quality 2000 to 3000 watt pure sine inverter is the typical range for rooftop AC. Expect about 5 to 12 percent loss through the inverter. Direct 12 or 24 volt DC air conditioners avoid inverter loss, run variable speed compressors, and can cut average draw in half compared to older ACs at the same comfort level.

How long will batteries run AC

Let us walk through practical examples.

• Small DC unit example: A high efficiency 12 volt DC air conditioner averaging 600 watts across the hour will consume 0.6 kWh per hour. A 5 kWh lithium bank can support about 8 hours before charge.
• Standard rooftop example: A 13.5k BTU 120 volt rooftop AC consuming 1400 watts when on and 50 percent duty cycle averages about 0.7 kWh per hour. The same 5 kWh bank yields about 6 to 7 hours.
• Peak heat scenario: If the compressor runs nearly continuous at 1400 watts, that is 1.4 kWh per hour. A 5 kWh bank offers about 3 to 3.5 hours.
• Higher voltage systems: Moving to 24 or 48 volt battery architecture reduces current, eases cabling, and improves inverter performance under heavy loads. Runtime in kWh terms is the same, but efficiency and component life improve.

A simple formula helps with planning. Runtime hours equals battery kWh divided by AC kW, then multiply by one minus expected loss, then multiply by duty cycle if cycling. Remember that real world heat load changes with sun, insulation, and setpoint. It is normal to see double the runtime at night compared to afternoon.

Charging makes or breaks the plan

Solar, alternator, and shore power work together. A typical van roof holds 400 to 800 watts of solar, which can offset 0.4 to 0.8 kWh per hour at midday. That slows the drop but rarely runs the AC by itself. A modern secondary alternator or high output DC to DC charger can feed 30 to 120 amps, refilling the bank while driving. Shore power tops the list for long stays, and a small generator is a last resort for extreme heat or extended boondocking.

Efficiency moves that stretch hours

• Insulate well and seal air leaks to reduce heat gain.
• Use window covers with reflective cores on sun sides.
• Park in shade, point the biggest glass away from the sun.
• Pre cool the cabin before the hottest window of the day.
• Lower the setpoint only as needed and use auto fan.
• Run a low draw fan to reduce perceived temperature.
• Keep the return filter clean to reduce compressor work.

Safety and component ratings

Verify the battery management system continuous discharge rating supports the AC load. Use short, properly sized cables, class T fusing, and a main disconnect. Vent battery compartments as required by code for your chemistry and follow manufacturer clearances for inverters and chargers. Secure all components to withstand hard stops and rough roads.

System design checklist for battery powered AC

• Select the AC type. High efficiency DC units offer lower average draw and smoother cycling. If using 120 volt AC, add a soft start.
• Size the battery bank in kWh based on your target runtime in the hottest likely climate.
• Pick the inverter size for surge and running loads, leaving headroom for other appliances.
• Map your charging profile. Combine alternator charging, realistic solar, and shore options that match your travel pattern.
• Add monitoring. A shunt based battery monitor and temperature sensors help you steer setpoints and know when to recharge.
• Plan airflow. Keep return paths clear and duct cold air where you sleep to improve comfort at higher setpoints.

Bring it together with a pro build

If you want cool air that just works, the best results come from a system designed as a whole. Battery size, AC type, inverter output, wire routing, and charge sources need to be balanced to your travel style. Our team builds complete vans and integrates climate control that keeps trips comfortable and quiet, without oversizing or guesswork. Explore our Recreational adventure vans to see how a finished system comes together.

Need a cabin that sleeps cool in summer and sips power at night? We plan, fabricate, and install power systems, rooftop or DC air conditioners, alternator charging, and control panels that are simple to use. For a start to finish experience tailored to your route and climate, check our Custom build van process. If you are comparing platforms that finance and want an AC ready canvas, visit Mainstream vans that finance.

Ready for battery powered cooling that matches your miles, seasons, and budget? Use the form below. We will translate your comfort goals into a precise electrical and climate package, schedule the work, and hand you the keys with a walkthrough and on site shakedown.

At OZK Customs we design and build Recreational Adventure Vans, Overland rigs, and Commercial vans with integrated climate and power. Our shop in Fayetteville Arkansas delivers complete custom builds and partial upfits with tested components, clean wiring, and clear documentation so your air conditioning performs on the hottest days and the quiet nights alike.