Please help me get to the grocery store!
September 24, 2011 9:28 PM   Subscribe

Can I jump start my car battery from my motorcycle?

My car battery has been dead for a week. The battery was brand new last month and I believe it died because the trunk latch was broken and the trunk light was on for a weekend in which I didn't drive. The trunk latch has now been fixed and the trunk stays closed.

I don't have anyone I can call on to help with this before Monday at the earliest and I'd rather not pay a towing company if I can avoid it. I don't have AAA.

I do have jumper cables and a motorcycle with a battery that was new in the past year. I like tinkering and am comfortable with tools and such. The car is a 4-cylinder 2000 Acura Integra with a manual transmission.

Is this doable? If so what will be different than the car-to-car method?

Thanks for your help!
posted by bendy to Travel & Transportation (34 answers total) 1 user marked this as a favorite
Best answer: Yes, it's possible. Probable? I don't know. Whats the amp rating on the motorcycle battery? I bet it's more than enough to get a car going. Hell they have lighter plugin things that jump car batteries all over and they work. This is the sort of thing I'd just do.
posted by sanka at 9:41 PM on September 24, 2011

If the bike is 12v, then it should work. Make sure the bike's running, of course. That said, if it's a manual, would it perhaps be simpler to just roll-start?
posted by pompomtom at 9:43 PM on September 24, 2011

Is it possible? Yes, it's possible. Is it advisable? Probably not more than once, and I'd be wary of trying to recharge the motorcycle battery with anything other than a trickle charger; that is, I think recharging it with the bike might put too great a load on the bike's charging system. At the very least, let the car charge the bike battery back up.

With all that said, can you push-start the car? It shouldn't take much to do.
posted by TheNewWazoo at 9:45 PM on September 24, 2011

Tough call. If it's a 12V bike it should work, but most motorcycle batteries have about 1/3 the CCA rating of a car battery, so even with the bike running, it may not be enough.
posted by xedrik at 9:46 PM on September 24, 2011

Response by poster: Push starting the car would be possible if I had someone to help me - trying to do it myself probably wouldn't end well.

Im tempted to just try it. If it didn't work, is there any chance it would damage the bike's electrical system?
posted by bendy at 9:59 PM on September 24, 2011

It might be easier and more reliable to find a friend or neighbor with a car, since you already have the jumper cables. It only takes a couple of minutes, so it shouldn't be too hard to find someone willing to help.
posted by zachlipton at 10:01 PM on September 24, 2011

Best answer: There is a very real possibility, IMHO, that doing so could damage the stator or the regulator/rectifier. If you must, I would very highly recommend revving the bike to 4-5k RPM in order to ensure that maximum current is available while you try it.

Not to derail too badly, but I've push-started a car myself a couple of times on level ground. If you've got the space, it's maybe worth a shot.
posted by TheNewWazoo at 10:03 PM on September 24, 2011

I don't think you'd damage the bike electrical at all just giving it a go. But I advised just hooking it up and giving it a go in the first place.
posted by sanka at 10:15 PM on September 24, 2011

Best answer: Yeah, you might could damage your motorcycle's battery and/or charging system. Depends on how "dead" the car battery is. If its voltage is just a bit below what will start the car, the cycle battery might be able to supply enough charge. But if the trunk light drained the battery pretty low, I'd think twice before I tried it, the problem being that a completely discharged battery is like a dead short across the good battery.

Better: You could just remove the battery from the car and take it (on your motorcycle) to someplace that can charge it for you.
posted by exphysicist345 at 10:25 PM on September 24, 2011 [1 favorite]

Response by poster: I don't think there's room in the parking lot to push start the car myself. First I'd have to back it out of the space without hitting the cars behind it.

Ideally I want to get this done tomorrow and I'm newish in town and don't know anyone well enough to ask for help.

I have a tender for motorcycle batteries that says it outputs 12V @ 750mA and the input is specified as 120 VAC @ 60Hz 20W. If I put the car battery on this will it charge enough to start?

Electricity confuses me. Thanks for all the suggestions.
posted by bendy at 10:41 PM on September 24, 2011

Best answer: That battery charger will totally restore your car battery, but depending on how dead it is, that could take several days to do so. (750 mA is not very much).
posted by aubilenon at 11:05 PM on September 24, 2011

Best answer: Oh snap! Yeah, hey it is worth a shot, right? Toss it on the charger and give it a try in the morning.
posted by TheNewWazoo at 11:26 PM on September 24, 2011

Response by poster: OK, I brought the battery in and put it on the trickle charger. One of my co-workers did come over and jump it Tuesday at lunch time but I didn't leave it running long enough and it died again that night with a with a fanfare from the alarm.

Got my fingers crossed it'll recharge within 24 hours or so. Now I'm going to get a beer or three and raise a toast to all you helpful people.
posted by bendy at 11:33 PM on September 24, 2011

Best answer: ...if it doesn't work, one last angle to try: in my city, most cab companies will have a driver come out and jump your dead car for you, and the charge is not unreasonable (like $15). I have no idea if this is standard or if it is just a strange Anchorage thing, however.
posted by charmedimsure at 12:16 AM on September 25, 2011 [2 favorites]

Response by poster: charmedimsure: that's also an amazingly great idea and it totally plays into my stubborn refusal to ask anyone for help unless I can pay them. I'll see what happens with the trickle charger and go from there.
posted by bendy at 12:58 AM on September 25, 2011

I did what charmedimsure did and it was in europe so it's not just an AK thing i guess..
posted by 3mendo at 1:37 AM on September 25, 2011

Don't miss this opportunity to connect with a new neighbour! Seriously! "Knock, knock, hi, I just moved in and don't know anyone in town yet and... can you help me jumpstart my car?"
posted by seanmpuckett at 5:44 AM on September 25, 2011 [1 favorite]

Best answer: My push-start technique isn't to do it myself: it's to ask the first strapping young lad(s) who walk by if they'd give me a hand. Most guys would jump at the chance to impress someone with a feat of strength. Plus, pushing a car is fun and comical, two other reasons which will very likely compel someone to propel you.
posted by matlock expressway at 7:49 AM on September 25, 2011 [1 favorite]

fyi on push starting: this can dump raw fuel into the exhaust, which can destroy the catalytic convertor, so thats a pricey option if you live somewhere with smog laws...
posted by davejay at 2:02 PM on September 25, 2011

I uh, what? How does it dump any more fuel than simply starting with a weak battery? If the engine's turning under ~300 RPM, the ECU knows it's in "cranking" mode, and reacts accordingly, whether it's the starter or the wheels turning the engine. Aside from that, why would a tiny amount of raw fuel hurt a catalytic converter? Especially as the cat won't actually be reacting with the fuel yet, and the exhaust gasses will be relatively cold in contrast to the normal "too much fuel kills cats" scenario, which is an excessively rich mixture after the cat has fired off.

Push start with alacrity, I say.
posted by TheNewWazoo at 4:47 PM on September 25, 2011

Best answer: If the battery is really, really flat, then not only will it not have enough grunt to turn over a starter motor but it will probably not even be able to run the ignition system, which means that push starting will do no good.

A new car battery will generally have a charge capacity of about 55 amp-hours. If it's got at least five amp-hours of charge in it, it will probably start a car. About 70% of the charge you push into a battery will generally stay there; the rest is wasted as heat. So if you run 750mA into a dead flat battery for twelve hours, that's 3/4 amp times 12 hours = 9 amp-hours of supplied charge, of which the battery will retain 70% of 9 amp-hours = ~6 amp-hours, which should give it enough for a couple of starts.

I didn't leave it running long enough and it died again that night with a with a fanfare from the alarm

Sounds to me as if something is still discharging it as it's parked. I wouldn't expect the alarm alone to draw enough to do that, so it would probably pay you to visit an auto electrician and have the leak tracked down.
posted by flabdablet at 6:22 PM on September 25, 2011

Response by poster: I thought that it was necessary after getting a jump to leave the engine running for 45 minutes to an hour? Last month my (old) battery was dying and I had it jumped three times in one day - at least one of the people who helped me told me that.
posted by bendy at 8:05 PM on September 25, 2011

Response by poster: PS. The battery is still on the trickle charger and the light is still red, but I've had too much beer to take take it driving for an hour now if the car will even start. I will try it tomorrow night after i come home from work, at that point it will have been on the trickle charger for not quite 48 hours.
posted by bendy at 8:08 PM on September 25, 2011

Can I ask why you don't just buy a real battery charger? $30-$40 dollars should buy you plenty of charger, and then the next time this happens, you just throw the charger on it and you're good. A decent battery charger can bring the battery back to full charge in 6-8 hours.
posted by cosmicbandito at 8:19 PM on September 25, 2011

Response by poster: cosmicbandito: I always try to find the least expensive solution and the one that makes me acquire the least stuff. I went to the auto parts store on Saturday and chose to buy the $32 jumper cables instead of the $60 battery charging machine. My $20 motorcycle trickle-charger will do the job in a couple days and that's fine with me since I've got a moto I can ride in the meantime. Most of this question was about me looking for creative, tinker-y solutions to a small problem that doesn't cause me much stress - I have no sense of urgency about this.
posted by bendy at 8:48 PM on September 25, 2011

Response by poster: matlock expressway: i love your approach and appreciate the propulsion compulsion. I'm just a little shy about approaching the strapping lads most of the time. Maybe I should be loitering in the parking lot more often.
posted by bendy at 8:54 PM on September 25, 2011

Best answer: I thought that it was necessary after getting a jump to leave the engine running for 45 minutes to an hour?

Your car's alternator is built to push maybe 20 amps into your battery, which means that running your car for an hour would bring a typical 55Ah battery to somewhere near one third charged from dead flat. That should be more than enough for a bunch of regular starts, or a handful of nasty cold starts.

Running a car battery down to dead flat is not good for it, and neither is leaving it flat. So running your engine for long enough to get a fair amount of charge in after needing a jump start is indeed a good idea.

But even if your battery had the maybe 5% charge you'd have from a jump start followed by a short run, it should hold that charge overnight. Might not be quite enough for a start, but should still have been plenty to run only the car alarm overnight. That's why I'd be having it checked to make sure nothing else is draining it.

48 hours on that trickle charger will have delivered 36 amp-hours to your battery, of which it will have retained probably 20Ah. If there's nothing draining it while you're parked, that should be plenty to keep you going. You shouldn't need to drive it for an hour just for the battery's sake; it should charge itself back to full again over the next few days of normal use.
posted by flabdablet at 8:59 PM on September 25, 2011

Response by poster: So, tomorrow night I will come home from work. I will grab my car battery that has been sitting on my kitchen floor on the trickle charger for about 45 hours. I will put it into my car (10mm socket BTW) and (IF IT STARTS UP) I will drive around for about an hour, maybe more. If I need dinner, I will go to the In-n-Out drive-thru, perhaps in Daly City. I will drive to Half Moon Bay and back. I will take a miniature road trip without shutting off the car. Tuesday morning, I'll be able to drive my car to work. Keep your fingers crossed.
posted by bendy at 9:18 PM on September 25, 2011

Best answer: A start goes for maybe ten seconds and pulls about 200 amps. So that's (200 amps * 10 seconds ÷ 60 seconds/minute ÷ 60 minutes/hour) = 0.5Ah, say 1Ah effective because at 200 amps the battery is much less efficient.

So if you've trickle-charged 20Ah in there, and you prove it works with a start that uses maybe 1Ah, you've still got plenty more starts even if you don't drive it around. You should definitely do a trial start, just to rule out the possibility that the battery is a lemon that one deep discharge has killed. If it is, you have time to replace it before Tuesday morning.

But there is still some doubt in my mind about your car's ability to remain parked without draining the battery. If your car were my car, and I absolutely needed it to start on Tuesday morning, and the battery did indeed prove itself capable of a trial start, I would not be driving around all over; I'd have the battery back out and back on the trickle charger Monday night, and I'd be heading to the auto elec to check out the parked discharge current after work on Tuesday.

If you don't feel like trickle charging it Monday night, at the very least keep the wrench in the car and disconnect one battery cable after parking it. Yes this will kill your alarm, but it will also immobilize the car :-)
posted by flabdablet at 9:43 PM on September 25, 2011

Response by poster: Thanks flabadablet. The car is my mortal enemy. I only need it on occasion and if it doesn't start I turn up my nose and move to my preferred method of transportation, the motorcycle. I do sometimes need to visit the Home Depot for a large purchase, or the grocery store for a big shop and there doesn't seem to be a convenient Zipcar here on the peninsula. At the same time, there are ways of securing big things to the motobike.

If it starts Monday night I'll be psyched. If it doesn't start after another day of charging the battery I'll have to make the choice between bringing it to a mechanic or donating it for a tax write-off. At this point I could go either way.

Frankly the alarm is a burden. I half-wish someone will steal the car and I can get a few bucks for it.

In my investigation this weekend, since I bought the battery from an AAA tow truck (my sister was here visiting and I used her card), apparently the battery has a 3-year warranty? Maybe I can call the 800 number and get this fixed that way.

Again, I was looking for creative, tinker-y solutions, but maybe I should have been a little more observant... Thanks, all, for your patience.
posted by bendy at 11:25 PM on September 25, 2011

Best answer: If the battery dies again, there's a pretty easy (and tinkery) way to determine what's killing it.

Get a 12 volt test light (any light designed for 12 volts will work, you could even pull out a blinker bulb temporarily). Disconnect one battery cable (doesn't matter which one) and connect the light between the cable and the battery.

This should probably be done at night, as it shouldn't light up very brightly at all.

The idea is that any current that is being drained off the battery will have to go through the light bulb. The brighter it lights up, the more of a drain there is on the battery.

Now pull fuses (one at a time) until the light goes out (or gets much dimmer). Presto! You've found out which circuit is draining your battery.
posted by Dorri732 at 6:34 AM on September 26, 2011

The car is my mortal enemy. I only need it on occasion and if it doesn't start I turn up my nose...

Have you actually gone through the exercise of comparing what it cost you to own your car last year with what it would have cost you to use taxis and/or hire cars for the same trips?

If it does actually turn out that having your present car available for infrequent use is cost-effective, the easiest thing you can do to keep it reliable is lend it to a commuting friend. Next easiest is to take it for a half-hour drive once per week. Both of these schemes will make sure the battery stays topped up, your fuel doesn't go stale, your brakes don't dry out and your oil channels don't silt up.
posted by flabdablet at 3:14 AM on September 28, 2011

An alternative to loaning it to a friend is something like RelayRides, which is in SF.
posted by TheNewWazoo at 6:41 AM on September 28, 2011

Response by poster: I just came back to this question after a few days... yes, I do actually use the car to drive the 1.4 miles to and from work every weekday. When I shift into "my perfect life" mode, I'll be biking to and from work and this won't be an issue. In the meantime I'll stick with it.

RelayRides is awesome but here on the peninsula, people are way less interested in programs like that since they all have their own cars. I still maintain a healthy hatred of cars after living ten years in the city, but I'm definitely the minority here.
posted by bendy at 9:58 PM on October 6, 2011

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