Running accessories


I read the recent newspaper column about engine idling, and I want to know if it is better to run accessories with the engine idling or with the key in the accessory position. Will extended use in this mode hurt the battery? What about leaving 12-volt plugs for cell phones and coolers plugged in when the car is turned off? I have a new conversion van with TV and other electronics. What’s the best way to use them?


Leaving the key in the ACC position will kill the battery quite quickly when you have large power draws, like a TV. Also, many vehicles (all mine do, anyway) cut accessory power when the key is in the OFF position; chargers and whatnot don’t work when the key is off.

However, you’d be fine to watch TV with the key in the ACC position as long as you occaisionally start the van up to recharge the battery.


What you really should have is a separate battery to power the accessories while you are parked and the engine is off. This would spare the main battery so it would always be able to start the engine.

There are systems available to install and wire additional batteries. Check camping supply stores or maybe RV dealers.


Check the wattage of the accessory, if possible. A low-wattage accessory such as a cell phone charger or the car’s orginal stereo, can be operated many hours, even overnight, from the ACC position. A high-wattage accessory such as a TV or cooler may run down the battery in a few hours.

The problem with this advice is that you never know when your car’s battery is approaching a critical state. Cross the line and you will have a no-start condition.

One solution is to buy a portable jump start unit. You can either run your 12v accessories of this item, or run them off the car’s battery knowing you always have backup starting power.


The people that built the conversion van might have some answers for you. We really don’t have enough information to give you full advice. If you are going to do this on a regular basis and have coolers running for a long time, you might be best off installing an isolated auxiliary battery and increasing the capacity of the charging system. Since this is a van, it might be relatively easy to install a bigger alternator. It is done all the time with ambulances and such. I am surprised it was not offered as an option for the conversion, though I don’t know that much about the conversion market.

You could also go to an automotive electrical shop. They could fix you up for sure. If you are running a lot of power-hungry accessories, you would be best off with an auxiliary generator.