Does a power inverter drain car battery?

Adding a power inverter to your car, truck or motorhome can greatly expand the number of electronic devices you can use on the go, but nothing in life is free. If the power comes from a starter battery, it has risk to drain your battery. The general rule is that an inverter does not drain the battery when the car is running, and especially not when the car is in motion. However, if you use the inverter to power devices when the engine is off, the battery will be discharged and the worst is that the engine cannot be started.

1.Power inverter may drain the battery when the engine is running

When the engine of a car or truck is running, the alternator charges the battery and provides power to the electrical system. Meanwhile, the battery also plays very important role because the alternator needs voltage from the battery to work properly.

When everything is working properly, the alternator charges the battery when it needs charging, provides power to electrical systems and components like the stereo lights and air condition, and the alternator leaves power for accessories like the inverter.

If the alternator is unable to provide this power - either because it fails or because it is not powerful enough - the electrical system can fail. If this condition continues for too long, the battery will eventually become so depleted that it no longer has enough power to operate the vehicle's electronic systems. At this point, you may have problem to start the car, even the engine may die.

2.Power inverter may kill the battery when the engine is off

When the engine is not running, the battery is responsible for powering the electrical system. So if you leave the inverter on during parking, the battery will be completely discharged, in the long round, the battery will die. Since the starter motor requires a large current to start, using the inverter while camping may cause big trouble.

If you use an inverter while camping, you should buy an extra battery to make sure you have enough power to run the inverter. You can also take a generator with a built-in charger in case you need to run the engine from time to time to charge the battery.

3.How fast will power inverter drain battery?

The length of time your batteries will be drained is proportionate to the capacity of the battery, the load that connected to your inverter, whether the battery is being charged or not. These will cause different result.(Please take note that most batteries, especially those with circuits, will not drain down to 0 Volts , otherwise it will shorter the battery life, even kill the battery)

If you are using the same 20Ah battery to power 3 different devices, they draw 20A, 10A and 2A power from the battery, the lasting hour will be different. It can be t 1 hour or 2 hours, or even 10 hours.

Let’s show you a detailed example：

A 100Ah battery power an appliance that draw 10A, then you can get the battery lasting hour:

Battery Capacity/Discharging Current=Discharging Time

100Ah/10A=10 Hours

This is the time in theory, we also need consider the power loss, the charge efficiency, etc, so we need multiple the hours by 0.8 or 0.9 to get closer to the actual time.

Many devices are sized by wattage which you can read from the labels.

This specification also can help to get the battery lasting time.

Let’s take another example:

12V 80Ah battery, 16W laptop, 4W bulb and 200W TV,

how long can these appliances keep working?

Discharging Time=Battery Capacity*Battery Volt*0.9/Devices watt

80Ah*12V*0.9/90W=9.6Hours