Plan to Connect an Inverter to the Car Battery? Read this First.

If you want to power an AC appliance while on the road in your car or truck then you should consider getting a power inverter.

Power inverters come in different sizes and power output capabilities (watts) which begs the question, what size of inverter (watts) should you connect to the car battery? How long can you expect it to last?

Read on to learn what size of inverter you should connect to the car battery, tips that can help minimize battery drain by the inverter, and alternative sources of power for your AC appliances instead of using an inverter.

Can You Use an Inverter on a Car Battery?

Yes, you can use the car battery to provide DC power to your inverter.

If you’re connecting the inverter to a starter battery, it is best to limit its capacity (watts) and duration to avoid discharging the car battery and leaving it without enough power to start the engine.

For example, a 150-watt inverter at maximum capacity can use about 50% of the capacity of a 45-60 Ah car battery in two hours!

Check out ways you can minimize the drain on the car started battery.

Does an Inverter Drain a Car Battery?

Yes, an inverter draws power from the car battery even when no appliance is connected provided it is switched On.

For example, a 150-watt inverter plugged into a cigarette lighter socket draws approximately 180 mA when no appliance is connected.

Though it is a fraction (less than 2%) of its rated current, over time it adds up and can drain the car battery.

How to Minimize Inverter Power Draw on a Car battery

#1. Switch off the inverter to avoid power drawn by the inverter from the battery when the inverter is not in use.

#2. Use the inverter’s low-power mode (where available). Switch On the low power mode on the inverter if your inverter has one (consult the inverter manual).

Whereas it does not stop the inverter power draw when no appliance is connected completely, it significantly reduces it in some cases by up to 80%.

#3. Keep the engine running. If running a power inverter, keep the engine running to minimize the power draw from the battery.

By doing so, the power to run the inverter is supplied first by the alternator and only from the battery should the alternator power not be enough.

#4. Use a high output alternator. Consider installing a high output alternator of 200 amps or larger if you plan to power a large inverter in your car or truck to meet the inverter power needs without drawing any power from the battery.

What Size of Inverter to Use in your Car

If you plan to connect the inverter to the car’s cigarette lighter socket, you’ll need to limit the connected inverter to about 120 -150 watts depending on the allowed maximum current draw of your car’s cigarette lighter socket. (Check your car’s owner manual).

If the car has a 55Ah battery, you can expect the 150-watt inverter to run for about 1-2 hours (estimate) depending on the age and condition of the battery.

Note: Assumes the car engine is not running.

If you need to connect a higher power inverter, you’ll need to hard-wire (install additional, dedicated wiring and fuses) to the car battery.

Additionally, install a separate car battery to mitigate the risk of the inverter draining the car starter battery.

Related questions

#1. Can a Car Alternator Power the Inverter?

Yes, a car alternator can power an inverter. In fact, if the engine is running while the inverter is switched on and powering appliances, the power is drawn from the alternator first.

Therefore should you need to power a large inverter from your car or truck, install a high-output alternator.

#2. How Long a Car Battery Lasts with a 400 watt and 2,000 watt Inverter

Assuming a fully charged 12V, 60Ah battery, then a 400 watt inverter running at maximum capacity will drain the car battery to 50% of its capacity in under an hour. This of course assumes the battery is in good condition.

Older and aging batteries will last for a shorter time.

A 2,000-watt, 12V battery draws about 166 amps at full load. You’d need to check the battery specifications if this current level is within the recommended current draw from the battery.

For large output inverters, consider installing a high output car alternator and keep the engine running or invest in a generator.

Alternatives to Using an Inverter to Power Appliances in your Car

If you plan to power larger appliances that require a 1,000 watt + inverter, consider purchasing a generator instead.

It provides more power for the investment (compared to the cost of an inverter + battery bank) but has the disadvantage of being noisy and requires regular maintenance.

Final Thoughts

Power inverters can drain the car battery provided they are switched on and the car engine is not running.

To minimize power draw by the inverter, keep the engine running.

If you plan to connect the inverter to the cigarette lighter socket, you’d need to limit its power rating, for example, 180 watts for a 15 amp cigarette lighter socket.

How long a car battery lasts with an inverter depends on the inverter size and battery capacity, state of charge, and condition.

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