Thanks to the widely available cigarette lighter port in many cars, you’re now able to power your 12V accessories reliably.
As with most appliances, you need to be aware of the dos and don’t to get the best of out them.
For example, should you leave the cigarette lighter adapter plugged in overnight? Will it drain the battery? Reasonable concerns if you ask me.
So, this post sheds light on if and whether an adapter can drain a car battery and shares suggestions on how to prevent your battery from draining.
Will a Cigarette Lighter Adapter Drain the Battery?
Unfortunately, there is no straightforward answer as it depends on on whether the port remains powered overnight even when the ignition is off and whether there is an accessory is plugged in.
Cigarette lighter adapter with a LED indicator Light
That notwithstanding, some adapters have a small LED indicator to show whether the adapter is powered or not.
This LED draws currents of a few mA (under a 1 watt), not to the level that you should be worried about unless the car is parked for several days or weeks.
Cigarette lighter adapter with an accessory plugged in
If on the other hand, an accessory is plugged into a cigarette lighter, for example, a power inverter, 12V fan or it is charging a phone and the port is always on (regardless of whether the ignition is on or off), then there can be a considerable current draw.
For example, if up to 150 watts are connected to the port, then a 50Ah battery can be drained to 50% of its capacity in about 2 hours.
Note: There is no current draw If the port is powered off when the ignition is off.
#1. Does a USB Charger Drain the Battery?
No, if no accessory (phone, inverter, or other) is plugged into it. If an accessory is plugged into it and the cigarette lighter port is powered then the car battery can be drained.
Note though that a charger with a LED indicator can consume a little power (typically under a watt) which should not be an issue if the car is driven regularly and the battery is charged.
#2. Should you Leave Accessories Plugged into the Cigarette Lighter Port? Does it Drain the Battery?
In my opinion, not a good idea unless you’re sure that the cigarette lighter port is powered down when the car’s ignition is off.
Doing so risks adding to the drain by the car alarms and sensors that stay powered if the cigarette port is always powered. Check the car owner’s manual to confirm whether the port stays powered or not when the ignition is off.
Tips to Prevent Car Battery Drain
To prevent your battery from being drained when an accessory is plugged into the cigarette lighter socket:
#1. Keep the engine running if you’ve got an accessory such as a laptop plugged into the port. With accessories such as phones, the power draw is considerably lower, and depending on the charge level of the battery, the drain may not be significant if used only for a few hours.
#2. Unplug the charger or adapter if in doubt whether the socket is always on. Some ports (sockets) are always on regardless of whether the ignition is on or off while others power down after a set period of the ignition being turned off, say 30 minutes. If not sure, simply unplug the adapter.
#3. Connect the car battery to a battery maintainer. Regardless of whether an accessory is plugged into the cigarette lighter adaptor or not, most car batteries will be drained anyway from self-discharge or by the onboard electronics such as sensors or car alarms that are always on.
If you’re driving the car regularly, this is usually not an issue.
However, if the car is left parked for a few days or longer depending on the condition and state of charge of the battery, you risk draining the battery. In this case, get yourself a car battery maintainer to keep the car battery topped up.
A cigarette lighter charger or adaptor by itself will have a minimal drain (if it has a small LED) otherwise there is no drain if no accessory is plugged in. This assumes that the cigarette lighter socket is powered.