car talk question

[lI1|1!]

'89 nissan pathfinder

 

ok so this is a pretty basic question - my battery is dead (as in putting on a charger overnight doesn't charge it) so i'm buying a new battery later today.

 

here's the question parts:

 

1) i just replaced the battery about a year ago. i had purchased a cheapo one as it's an older car and i don't like to sink money into it. but now i'm thinking it's worth it to spend more and avoid the hassles. what do i look for in a battery that will last more than a year? when it died i was like 'can't be the battery i just replaced it' but abviously not. the car mostly just gets used on weekends, so sits idle for a week or two at a time, does that wear out a battery faster?

 

2) is my alternator killing my batteries? the alternator light has never come on in all this (if it still works), but should i take it into the shop and have them check the alternator or whatever?

 

thanks in advance

[fenderfour]

You don't need to take your car to the repair shop, just a Schucks or Napa. They can usually test the alternator in the car.

[catbirdseat]

If you have a multi-tester you can check out the voltage put out by the alternator yourself. If you alternator is putting out insufficient current or voltage (or too much) your battery will not last as long.

 

I don't know how to check for this but occasionally cars will have minor shorts that can drain a battery as the car sits. If the car doesn't get used often, as you say, even small drains can be significant. It could be a small light staying on in the trunk or glove box, even.

 

Leaving the lights on, to the point of needing a jump start, will kill a battery if you do it repeatedly.

Edited July 2, 2007 by catbirdseat

[whirlwind]

like fendor said shucks or napa can test it for free while its in the car, but ask lots of questions and maybe go to both places i've had shucks insist my batty was shot and told me i need to replace it, well a yr later it finally stoped taking a charge but mostly case the car was sitting for 2 months the battery finally died.

as far as batterys go, go to costco, they have the best prices i've seen and also have a lifetime warrty.

before you replace the battery take it in to shcucks and have them put it on thier tester, they also have a slow charge that sometimes can bring it back to life (in which case it maybe your alt.), and check the water level of the battery, at a yr old even a chepee should still work.

[archenemy]

It does sound like you have a drain on your battery. Even a cheap one shouldn't die in a year.

 

 

If you test it with a multimeter (or if they do that at Shucks for you), your meter should read 12 volts on the DC scale on an accurate reader when the neg cable is disconnected from the battery. IOW: Be sure you zero your meter first. Reconnect it to the ground cable (and expect a small drop from items that are still hot--but not much). But if it is under 9.5, you need a new batt.

 

Also test the charging system by measuring across the battery leads with the engine running.

If the meter is accurate, it should be 13-14 volts,or just a bit higher. In no case should it read less than 12 volts (assuming an accurate meter), or less than the voltage of the disconnected battery. If the charging system is crap, the batt gets weaker as teh engine draws voltage from it.

 

 

If it really is your alternator and it isn't charging at all, your car should go for about an hour before it dies (after you've charged it). If it ain't dead, it will run for longer (meaning that its just weak, not a goner).

 

 

Finally, check your fuses. All your electrical stuff runs through the fuse box, and you can disconnect each one individually while measuring the response. Your initial read would be low, and then when you hit on the right one causing the drain, the voltage will jump up.

 

Have a ball.

 

 

 

 

[whirlwind]

easy way to check the alt is to start the car and pull the negitive cable off the car should still run. wit hand without headlights, with headlights the engine will probly bog down alittle though

 

 

but not realy recamended, it old school and you can shock your self and or do other shit to the car.

Edited July 2, 2007 by wirlwind

[fenderfour]

If you test it with a multimeter (or if they do that at Shucks for you), your meter should read 12 volts on the DC scale on an accurate reader when the neg cable is disconnected from the battery. IOW: Be sure you zero your meter first. Reconnect it to the ground cable (and expect a small drop from items that are still hot--but not much). But if it is under 9.5, you need a new batt.

 

Have a ball.

 

 

One more thing - if you test your battery without starting your car, it will frequently have what is called a "surface charge". This will give you an inaccurately high voltage reading. Start the car, let it run for a few seconds, then test the battery.

[archenemy]

Are you trying to out-nerd me?

[TREETOAD]

To test for a load on the battery when the car is not running and everything is off, remove the negative battery cable and connect a voltmeter between the cable end and the negative terminal of the battery. ( you can also use a 12 volt bulb type tester connected the same way) If you measure a voltage or the bulb type tester lights up, then you have a load. The brighter the light or the higher the voltage is, the larger the load and the faster your battery will drain. Start unplugging fuses in your fuse box and when the light goes out or the voltmeter reads zero you will know what circuit to check for shorts or problems.

To test the alternator Stick your voltmeter across the battery terminals when the engine is running and then turn on your headlights and heater fan to put a load on the alternator. The voltmeter should jump up to no more that 15 volts with the engine reving around 1200 rpm or so. If it does not then your alternator is pooched. You can buy rebuild kits for them for around 20 bucks if you want to save some money, but usually the rebuild is the way to go.

Your battery should last way more than a year. If you drain a battery till it is dead too many times the sulfur particles in the electolite come out of solution and become lodged between the plates in the battery and this shorts them out causing a dead cell. You can sometimes equalize the battery by charging it at around 16 volts for a day or so and this will cause the solids to go back into solution. It is the shits when you can't trust your car to start at a trail head after four or five days in the bush. I carry a smaller gell cell battery in the back of my jeep just in case.

Edited July 2, 2007 by TREETOAD

[ketch]

Not quite, outnerding would be testing without a multimeter.

 

If you have a standard 12 volt bulb you can test for a short. Disconnect the negative lead. Then put the end terminal of the bulb on the battery post, hold the battery cable to the jacket of the bulb. If there is anything that would draw, the bulb will light.

 

Keep in mind that most modern cars have minor draws (IE clock, radio memory, electronic devices...) these will always show an indication but one can pull the fuse on them and track the short. A draw with high resistance will cause a dim glow on the bulb, A dead short will cause the light to come on full intensity. You will need to take it from there.

[fenderfour]

Are you trying to out-nerd me?

No, I've had to do this before and been mislead by chemistry and physics.

 

To test for a load on the battery when the car is not running and everything is off, remove the negative battery cable and connect a voltmeter between the cable end and the negative terminal of the battery. ( you can also use a 12 volt bulb type tester connected the same way) If you measure a voltage or the bulb type tester lights up, then you have a load. The brighter the light or the higher the voltage is, the larger the load and the faster your battery will drain. Start unplugging fuses in your fuse box and when the light goes out or the voltmeter reads zero you will know what circuit to check for shorts or problems.

 

This I've never done before. I bet it would isolate any drain pretty quickly. Thanks for the new trick.

[TREETOAD]

As you say it is not so good for new cars but then nobody can figure anything out on new cars anymore.

[TREETOAD]

As you say it is not so good for new cars but then nobody can figure anything out on new cars anymore.

[lI1|1!]

epilogue:

 

schucks warranteed the battery at a prorate (it was actually 6 months past the one year full warranty) such that i got a new battery for $15. they also tested my alternator and told me it was weak. i took the car to my usual mechanic who confirmed the diagnosis and is [pun] currently [/pun] replacing it.

 

thanks again for your assistance!

[TREETOAD]

Good one!!

[MarkMcJizzy]

easy way to check the alt is to start the car and pull the negitive cable off the car should still run.

 

Do not ever do this

 

This will remove the battery from the circuit, where it is needed to "temper" the voltage coming out of the regulator. This is a good way to fry your ignition chip and printed circuits. I learned the hard way.

[catbirdseat]

epilogue:

 

schucks warranteed the battery at a prorate (it was actually 6 months past the one year full warranty) such that i got a new battery for $15. they also tested my alternator and told me it was weak. i took the car to my usual mechanic who confirmed the diagnosis and is [pun] currently [/pun] replacing it.

 

thanks again for your assistance!

So long, and don't drive like my brother!

[Dechristo]

speaking of electrical problems in cars...