# how to test if car battery is not good?



## johnny13oi (Jul 28, 2007)

Hey guys, my car battery was completely dead a few weeks ago and I had to have another person jump start the car to get me home. Well I charged it back up with one of those car charger things and drove around to make sure it charged up fine and I also tightened the terminals. Well the car has been starting just fine for these past few weeks, but I will be going back and fourth about 150 miles at a time and won't use the car for about a few weeks at a time when I go back up for college. I would like to check to see if the battery is good before leaving so I can replace it if I have to. Thanks guys.


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## greg_in_canada (Jul 28, 2007)

Some autoparts stores will test your battery for you (for free).

I don't know the exact voltages but here is what I have done when I suspected my battery/charging system:

1) Start the car and get it to fast idle. Measure the voltage at the battery. Up to about 14 volts is okay I think. If it is much higher your regulator may be bad and overcharging (and killing the battery).

2) With the engine still running, turn on the head lights, fan, rear window defogger etc. Measure the battery voltage again. If it is below 13V then you may have a charging system problem that eventually runs your battery dead (in city driving).

3) Turn off engine but leave headlights etc on. The voltage will drop to 12-point-something. If it keeps dropping and goes below 12V then you may have a bad cell in your battery.

Maybe someone can give more detailed voltages rather than my ballpark ones.

[Edit: here's a link with some numbers: http://www.2carpros.com/how_to/battery.htm ]

Greg


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## half-watt (Jul 28, 2007)

greg_in_canada said:


> Some autoparts stores will test your battery for you (for free).
> 
> I don't know the exact voltages but here is what I have done when I suspected my battery/charging system:
> 
> ...






all fine tests in the first reply.


[disclaimer: the following suggestions come from an unlicensed "shade-tree" mechanic who has been working on a cars for 40+ years. if a REAL automobile technician chimes in here and contradicts anything below, do what i would do - take the REAL technician's advise. please note also, that as i've gotten older, i don't work on as many cars as when i was younger, so by today's standards of the last 10yrs or so, my experience if more limited and may not always be applicable.]



here's more that you should do.


try to conduct the following tests at around 70degF if at all possible as lower temps can affect the results. however, if you live in very cold climes, it might be more important to conduct the tests at lower temps, but that can affect the results. 



0) i'm going to skip what may be an important test method which a Pro would do as it involves applying draining off surface charge and then applying very specific loads to the battery. We'll leave that to the Pro, not that it's that difficult to do, i've found with my limited experience that the below tests are sufficient.




1) starting draws the most current. you will need a voltmeter to perform this test. since designs are different nowadays, do what you need to do to prevent the engine from starting when you crank the starter (this could be as simple as disconnecting the coil wire or more complicated for some coil on plug designs).

measure the battery voltage while cranking the starter. shouldn't fall below ~11.5V for a strong battery. around 10.5V you should check the electrolyte level and specific gravity (if you are able to) and recharge the battery. if it falls to ~9.5-9.7 V - replace the battery is my suggestion. i've found that they won't hold a charge when the cranking voltage gets that low (they also won't start - older american muscle at least, as they're turning over too slowly).


2) you will need an inexpensive BATTERY hydrometer (NOT the same as an anit-freeze/coolant hydrometer) to perform this test. if you are able to pop the caps off of the battery, measure the specific gravity. since the acid is mixed with water you [EDIT] WON'T [/EDIT] get a 1.42 specific gravity (the specific gravity of 16Normal sulfuric acid, if i recall correctly). anything above 1.24 should be 'ok', IMO.


3) last but not least (and it should really be the FIRST test that you do) is to inspect all of the battery connections for corrosion and to insure that they are tight. inspect the engines individual belts or serpentine belt while you're at it. also, inspect the underside of the hood for traces of fluid thrown up onto it by the rotating belt(s) when the engine is running. this can often be one of the first signs that you have a fluid leak. if you find traces of fluid on the underside of the hood, look around for the closest source(s) of fluid or areas nearest the belt(s) where fluid could have leaked and gotten onto the belt(s) and thus be flung onto the underside of the hood - not battery related, but a good thing to look for. Also, make note of your fluid reservoirs. Low fluid can mean a leak. In the case of the brakes, it could also mean that your brake pads are worn or very worn, so if you can't find any leaks in the braking system, don't just refill the reservoir, check the thickness of your brake pads (or have a Pro do it).


we did NOT cover testing the automotive charging system here. the first reply did address that a bit.

[Note: as i have "old-timers" and often have trouble recalling certain info, please double check my "numbers" with a more reliable, current, up to date source.]


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## MarNav1 (Jul 28, 2007)

Load test is the gold standard. Turn your headlights on with a voltmeter attached and you will see very quickly if its bad or not. Have fun!


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## half-watt (Jul 28, 2007)

MARNAV1 said:


> Load test is the gold standard. Turn your headlights on with a voltmeter attached and you will see very quickly if its bad or not. Have fun!



agreed LOAD TESTING is one of two proper tests and a very easy one to do.

"headlights" - that's a quick test. However...

keep in mind that a starter can draw 160amps or more in some vehicles. that will SUCK the battery voltage down much more than the 10-12amps or so that the headlights might draw.

sounds like you know your cars!!


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## BB (Jul 28, 2007)

My 2 cents... If the battery is more than a year old (and especially if the battery has been flat for more that a few days if new), replace it.

Every battery that I have seen that was either cranked to dead, dead because of lights left on, or because of non-operation and small loads (on-star type system, LowJack, etc.--in-laws' Lexus on-star+LowJack take about 0.185 amps)--it will fail again without warning--could be even just a few hours since the car was last run (like going shopping and coming back out to go home).

Car batteries are designed for high starting current and are not designed to be operated below about 80% state of charge (20% discharge).

Also, if your car does have electronic loads and sits for more than a couple weeks at a time, I would suggest getting a trickle charger (or a solar panel charger if no outlets nearby and you have sun available--i.e., not covered parking)...

For my in-laws' car, and a van I have--I have had problems with trickle chargers overcharging/boiling the batteries dry (but still needing to keep the batteries charged)... So, I take a lamp timer and set it for just an hour or four a day for replacement charging of what energy has been loss...

For example,

0.185 amps * 24 hours = 4.44 AmpHours per day...

With a 1 amp trickle charger, I set it for about 4-5 hours of on-time per day... So far, the battery water level has stayed up--and the car starts every time (month or two between use--as long as they remember to connect the charger--I was told by the dealer, that they sell a trickle charger installed because otherwise the cars need to be driven every couple of weeks to keep the battery up).

On my van, I only run it about 1 hour per day to make up for battery self discharge and its very light loads.

Still, check the water every so often with a trickle charger--even with a maintenance free battery (add distilled/de-ionized water only).

-Bill


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## half-watt (Jul 28, 2007)

BB said:


> Also, if your car does have electronic loads and sits for more than a couple weeks at a time, I would suggest getting a trickle charger (or a solar panel charger if no outlets nearby and you have sun available--i.e., not covered parking)...-Bill




Great idea BB! The best solution yet, IMO. With so many cars having remote keyless entry, and alarm systems, the need for such an arrangement as you're suggesting is more widespread than many might realize.


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## johnny13oi (Jul 28, 2007)

half-watt said:


> Great idea BB! The best solution yet, IMO. With so many cars having remote keyless entry, and alarm systems, the need for such an arrangement as you're suggesting is more widespread than many might realize.



I too agree with this however when my car will be sitting for weeks at a time will be in a parking garage where there is no sun nor is there an outlet to plug in. But when I do drive it, I'll drive for at least 3 hours a trip.


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## turkdc (Jul 28, 2007)

Try touching the terminals with your tongue and see if it tingles! :thinking:


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## johnny13oi (Jul 28, 2007)

turkdc said:


> Try touching the terminals with your tongue and see if it tingles! :thinking:



hahahah but they're so far apart. I don't know anyone who could possible have a tongue that's long enough for that.


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## BillBond (Jul 28, 2007)

If you do not have a volt meter and know how to use it,
take it to an autoparts store to put on one of their testers.


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## FlashKat (Jul 28, 2007)

How old is this battery?
What brand?


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## ADDICTED2LITE (Jul 29, 2007)

The proper way to check a battery is with a load tester. 
Most Autozone:shakehead or Oreilly stores have one, but most employees don't know how to interpret the readings. 

Load test the battery at half the CCA( cold cranking amps) for 15 seconds. The battery should hold 10 volts at the end of the test.

I have sent many bad batteries to "the zone" and they say they have to charge the battery to test it. After charging the battery, they stick a small 50 to 100 amp load and some have the "smart" computerized testers that most always say the battery is good. Most of the time the battery is bad according to the Load test described above. They refuse to accept the battery as dead, then I take it back to the shop and it wont even start a vehicle. Them AZ people really are a ripoff.:thumbsdow


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## TedTheLed (Jul 30, 2007)

Flashcat, good point. I'd say if it's 4 years old or more and you got the bucks assure yourself of a troublefree battery through college by getting a new one..

or




(about $80.00)


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## LiteFan (Jul 30, 2007)

I would just buy a battery. Interstate is probably the most reliable brand, but on the cheap note you can find car batteries for a little as 30 bucks. I say this because anything can happen with 3 weeks of non usage (like that small draw that you don't know about)


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## BB (Jul 30, 2007)

In the old'en days with old cars/trucks... We used to leave the negative terminal loose so that you could pop it off when one wire or another would fry or other electrical problem (wearing insulation, heat cracked insulation, start solenoid stuck cranking, etc.).

Pop your negative cable (reduce any clock/radio/etc. loads) and run a padlock and cable through the hood--and nobody is going to jump start that car. Might be worth doing when left for weeks at a time in a college parking lot.

-Bill


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## 270winchester (Jul 31, 2007)

BB said:


> In the old'en days with old cars/trucks... We used to leave the negative terminal loose so that you could pop it off when one wire or another would fry or other electrical problem (wearing insulation, heat cracked insulation, start solenoid stuck cranking, etc.).
> 
> Pop your negative cable (reduce any clock/radio/etc. loads) and run a padlock and cable through the good--and nobody is going to jump start that car. Might be worth doing when left for weeks at a time in a college parking lot.
> 
> -Bill



that's what I am doing after my car was stolen earlier this year, I'm also in the Bay Area. That and a club.


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## half-watt (Aug 1, 2007)

BB said:


> In the old'en days with old cars/trucks... We used to leave the negative terminal loose so that you could pop it off when one wire or another would fry or other electrical problem (wearing insulation, heat cracked insulation, start solenoid stuck cranking, etc.).




been there. done that. those were the bad ol' days.


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## greenlight (Aug 1, 2007)

Don't forget to check your alternator for proper voltage.


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## chesterqw (Aug 1, 2007)

use a digital multimeter?


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## jrmcferren (Aug 2, 2007)

half-watt said:


> Great idea BB! The best solution yet, IMO. With so many cars having remote keyless entry, and alarm systems, the need for such an arrangement as you're suggesting is more widespread than many might realize.



My Mom's 1997 Dodge Grand Caravan has a special fuse (and has this in the owners manual) that can be pulled to turn off ALL of these loads and recommended for use of the car is stored for a long period of time.


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## Handlobraesing (Aug 2, 2007)

Some cars will require a dealer reset (described in manual) after an extended battery removal.(such as disconnecting it for a week). Some might lose the security code for the radio.


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## johnny13oi (Aug 3, 2007)

I just found one of these in my garage. No idea how to use it except for the obvious voltage function.


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