Charging a Dead battery - can you do it without driving?

I am having a dispute with my dad. He says he can keep his battery charged 9doesn’t drive often) by just running the car in park at a high rpm. I say you actually have to drive the car around in gear for a while. i need a technical explanation to the answer, if I am right, or he will just deny the whole thing!

I’m not sure about the charging question, but I have other comments. First, idling a cold engine at high RPMs is causing a lot of engine wear. Second, not getting the car up to full operating temperature frequently is leaving moisture in the oil and the exhaust system, so he should follow the severe-service maintenance schedule and he should expect the exhaust system to have rust issues eventually. Overall this is a bad idea.

Yes, of course the battery will charge with just the engine running. Being in or out of gear has nothing to do with it.

This time your Dad is absolutely correct and you are dead wrong. Where did you ever get the crazy notion a car must be in motion for the electrical system to work?! Your instruments should show the battery is charging even when the engine is at idle.

The alternator current output capability is dependant on RPM. However, the alternator is fully capable of producing enough current at engine idle RPM to charge your battery. The reason people rev the donor engine during a jumpstart is to make the donor alternator capable of supporting both the running car AND the high current draw of the dead car. Under normal conditions (ex: the battery was able to start the engine), there is no need to rev your engine in neutral or drive around to recharge your battery. It would be far more efficient and economical to buy a battery charger that plugs into the wall than to run your engine…

Ok, we have two sides, why cant both be right? I am getting a sense that the battery is not keeping a charge. If the alternator is working properly, it will charge the battery at idle speed. If it is not working properly it will not charge adequately and may work properly when the engine is at a higher rpm. An alternator diagnotsic MAY determine this to be either way. If a diagnostic results in a good operating alternator and charging system components, then move to the battery as a week link in the process. Don’t bicker any more on this one, fix it and move on.

Other posters have mentioned how the alternator works so I will only state that it isn’t a good idea to run the car to charge a low battery. It puts needless stress on alternator and wastes fuel. Get a battery charger to charge the battery. I also suggest you get a low powered solar panel that can be put on the dash and face the sun to keep the battey up if the car is parked for long periods without starting it. If the cigarette lighter circuit is active with the ignition off you can plug it in there.

Yes it will charge the battery. No it will not destroy the car, but it will add some extra wear and with the price of gas (even the price a couple of years ago, it is an expensive way of recharging the battery. A cheap battery charger will do the job for much less. It will pay for itself in a short time.

First, idling a cold engine at high RPMs is causing a lot of engine wear.

Says who??? You can run at higher RPMs within seconds after the car warms up without doing any damage what-so-ever.

It will be done either way, but I would rather drive it. There are other parts that should be driven just to keep them from rusting in place.

Using the cars alternator to bring the battery to a fully charged state when starting from a low charge state(10.0V) is not cost/time effective.The car doesn’t have to be moving,the idle does not have to be high,just “off idle”.A loaded charging system test is done with the engine at 1500-2000 rpm (depending on what manual you use)I dont think your running the car at 1500 rpm in the driveway.The real question is does anything need to be done in regards to the batterys charge and a lack of vehicle use. You will get many opinions,several a week on this forum.It depends on what the parasitic draw on the battery is and how long the inactivity time is,combined with battery health and vehicle storage enviroment.You need to set some tighter parameters to get a quality technical answer.

Both are bad ideas, money and wear wise. Sorry, but you both loose this one.

It is much better for the alternator, and your wallet, to just hook up a smart battery charger and let the car sit for a few hours while the battery gets a full charge. If the battery is particularly flat, it is quite hard on the alternator. I’d rather replace a $40 charger than a $150 alternator plus labor.