Hey all,
So I’m borrowing my sister’s van, which has no alarm or automatic shutoff of any kind if the headlights are left on. I think you can all guess what happened… 
I left the headlights on for about two hours (maybe two hours and ten minutes?) I did happen to see them and went outside and turned them off in time. Here’s the issue: I’m in the middle of a lot of work at home that all has to be done in two days, and now is not a great time to take the van out and drive it around for half an hour. Can I leave it until morning, or will that have too much of a negative effect on the battery? All advice welcome!
I’m not an electrical engineer, but, do you or a neighbor own a battery tender? If so, I’d spend 5 minutes now to get it hooked up and you should be fine. You sound busy, so having a dead battery in the morning when you’re trying to leave would suck (I don’t think leaving it overnight is going to drain it any appreciably more, but if it’s already too low to start, would be nice to know now, and not tomorrow morning). If you live in a nice neighborhood, you could just leave it idling in the driveway for a bit.
No, that’s one of the things I need to get, and the neighbors are gone… the issue isn’t needing to be somewhere in the morning but rather just getting all the work done at home. I won’t need to leave until afternoon. And I know from sad past experience that if I have a half hour interruption for something like driving a car around, nothing effective will get done tonight. So it would be a lot better to leave it until the morning and start fresh, fitting the driving around to recharge the battery into the schedule that way.
You don’t have to drive around for the alternator to charge the batt. Like Ditka said, idling in the driveway should do (45 minutes?). If you’re in a garage, leave the door up a foot or so (if you pull your car in head first).
I was also going to say, leave it running for a while. But I’m not sure idling charges the battery. Is the voltage output from the alternator high enough on idle to do that? If somebody here knows, or you can look it up somewhere, great – but if it was me and I couldn’t find that out easily, I’d put a brick or something on the gas pedal to push the engine speed up to maybe 2000 rpm, just to be sure. Not real fast, mind you, just sort of like a cruising speed.
Idling should charge the battery, unless there is something wrong with your alternator.
But, turn off all accessories - fans, radio, lights, etc.
I know starting in the 80’s some cars started not charging at idle to help pass idle emission standards.(less parasitic drag)
This was a service bulletin, on checking charging systems ( you should see >13.7v@ idle). These cars needed 1500rpm or so to charge.
I don’t know if this spread throughout the industry, but it seems like a cheating,weasley, underhanded way to sneak past a law…so I’m guessing it’s S.O.P. now:D
If it starts easily right now, I wouldn’t worry about it at all.
This.
Unless the battery freezes tonight, no harm done. Do you live in LA, or Florida? If so, you will be fine. If you live in Barrow Point Alaska, not so much.
IHTH, 48.
yeah, no.
Yep, idling definitely charges a battery.
I have a digital voltmeter in my daily driver. And the voltage goes to somewhere between 13.5 V and 14 V immediately after I start the car. Which means the battery is being charged. I would assume this is true for all other cars that have alternators. (OTOH, I believe older cars with DC generators did not generate enough voltage at idle to charge the battery.)
Best thing would be to charge it, barring the ability to do so, or jump start opportunities, or calls to AAA. Shut it down and let the battery rest till it is needed. Don’t be tempted to try to start it right away the battery will recover some ability to provide greater starting current if allowed to sit.
This, again.
Seeing as it’s tomorrow already, and the OP isn’t back, I assume she’s been outside waiting for a jump start this whole time.
I left my lights on for about four hours the other day. Then let the car sit for another two hours before starting it to drive home. It was also below freezing. However, the battery is only about two months old. There were no problems, it started just as easily as when the battery is completely fresh, and I’ve not noticed any problems since.
My logic was, if the battery was almost dead, and only had one start left in it, I didn’t want to start it at a time that I couldn’t immediately start driving. If it was already too low to start, it didn’t really matter if I found out right away, or when I was ready to leave work.
If I’d been at home, I’d have put it on the battery tender.
be mindful that you don’t want to regularly task your alternator with re-charging a significantly discharged battery. there’s really no current regulation in most typical charging systems, so the battery will be pulling a relatively large amount of current initially which puts the alternator under a good bit of thermal stress. and heat is the #1 killer of alternators.
Update: the van started fine, and so far, it’s been driving fine too. It didn’t get down to any lower than maybe about 50 last night (Portland, OR), so that might have helped. Thanks for all the advice! 
Just plug the car in until it says the battery is full. 
I vividly remember having to plug cars in overnight in Minnesota so the oil pan wouldn’t freeze, but I don’t think that’s what you mean. :rolleyes: Who else remembers driving around with an extension cord hanging out of the front grille??
Which is it?
mmm
About 20 years ago I had a Mitsubishi Tredia and had some battery problems. I was told that my alternator wouldn’t recharge my battery adequately unless I drove the car some distance at more than 20 miles an hour. Interested to hear that cars these days will recharge a battery even when idling.