BlackShadow
Results 1 to 17 of 17

Thread: buying a used car battery

  1. #1
    Flashaholic* degarb's Avatar
    Join Date
    Oct 2007
    Location
    Akron, Ohio
    Posts
    1,198

    Default buying a used car battery

    I need to buy a used car battery, because of cost. ... I know measuring, not voltage, but max amperage a nimh AA can put out is a better indication of health (internal resistance); so, below 1.5 amp max and I can toss it out, as it will refuse to smart charge anyway.

    I would expect a lead acid battery (if comparable to nimh) would put out 24 amps on such a test (12 x 2 amps). My meter goes to 10 amps.

    How to properly test. (testing voltage before and been burned before).
    Some people are all lumens and no lux, while others are all lux and no lumens. Some just thank God they have neither.-- All of my lights have throw--some pretty darn far, into the garbage.

  2. #2
    Flashaholic* Russel's Avatar
    Join Date
    Jan 2009
    Location
    California
    Posts
    583

    Default Re: buying a used car battery

    The method I like to use to test a car battery is first measure static voltage just to see if it isn't already dead. Then measure specific gravity with a hydrometer (assuming the battery isn't sealed) and load test the battery with a hand held battery load tester. If it passes these tests the battery still has some usefull life in it, the question then is how much. The age of the battery could give you some idea, if it is known.

  3. #3
    Flashaholic
    Join Date
    Aug 2011
    Location
    MD
    Posts
    336

    Default Re: buying a used car battery

    Quote Originally Posted by Russel View Post
    The method I like to use to test a car battery is first measure static voltage just to see if it isn't already dead. Then measure specific gravity with a hydrometer (assuming the battery isn't sealed) and load test the battery with a hand held battery load tester. If it passes these tests the battery still has some usefull life in it, the question then is how much. The age of the battery could give you some idea, if it is known.
    Yes, so you don't get a sulfated battery.

    A lot of discarded car batteries are still good because of misdiagnoses.

  4. #4
    Flashaholic pyro's Avatar
    Join Date
    Aug 2003
    Location
    Germany
    Posts
    387

    Default Re: buying a used car battery

    24 amps would be insufficient.
    Depending on the size and type of the motor current while starting can easily reach 300 A for a short duration.

  5. #5
    *Flashaholic* Mr Happy's Avatar
    Join Date
    Nov 2007
    Location
    Southern California
    Posts
    5,390

    Default Re: buying a used car battery

    Quote Originally Posted by degarb View Post
    I would expect a lead acid battery (if comparable to nimh) would put out 24 amps on such a test (12 x 2 amps). My meter goes to 10 amps.
    Noooo!!!!!!

    Under no circumstances try to do a flash amps test of a car battery. If you are lucky you will only blow the fuse in the meter. If you are unlucky you will explode the meter, cause a fire or burn the house down.

    The official way to do a flash amps load test of a car battery is the so called "cranking amps test". This needs a proper battery load tester that a workshop will have. The result for a good battery should be somewhere between 100-200 amps.

    However, buying a used battery is a lottery and may be a false economy. Batteries need to be fresh when new, and have a working life of about 5 years. If the battery has been previously discarded, chances are it is no longer working properly and you will have wasted your money. You can buy a crap old battery many times over, or you can spend the same amount on a new battery and look after it. Is cost really that much of a problem?
    Tiefer, tiefer, irgendwo in der Tiefe gibt es ein Licht

  6. #6
    Flashaholic*
    Join Date
    Jul 2010
    Location
    Sydney, Australia
    Posts
    995

    Default Re: buying a used car battery

    I went to my local Scrap Metal Dealer to buy some AGM Batteries. I brought along my Voltmeter, but fortunately the manager offered me the use of their Discharge Current tester, so I bought batteries based on good open-circuit voltage and discharge current !

  7. #7
    Flashaholic varmint's Avatar
    Join Date
    Aug 2011
    Location
    Cash, Texas
    Posts
    375

    Default Re: buying a used car battery

    I have a neighbor that did just that 3 times and spent more than a new one, he now buys a new battery at the local xxmart with a 3 yr no questions asked full refund policy and returns them juat before the 3 yrs is up for a new one.

  8. #8
    Flashaholic gearhead1972's Avatar
    Join Date
    Mar 2011
    Location
    Kent, NY
    Posts
    154

    Default Re: buying a used car battery

    Are you 100% sure it is in fact the battery? Are your battery terminals completely clean? can yo jump start it? what is the running voltage 13.8 or so volts? How much is this used battery? you can get a cheapo at auto zone or sears for like $50-60 may not last too long or be the right size, but will most likely be more reliable then a used battery.

  9. #9
    Flashaholic* LEDAdd1ct's Avatar
    Join Date
    Jul 2007
    Location
    Hudson Valley
    Posts
    3,124

    Default Re: buying a used car battery

    Quote Originally Posted by varmint View Post
    I have a neighbor that did just that 3 times and spent more than a new one, he now buys a new battery at the local xxmart with a 3 yr no questions asked full refund policy and returns them juat before the 3 yrs is up for a new one.
    I know someone who does the exact same thing from that same anonymous department store.
    "...and the diode multiplied and grew in brightness. And God saw that it was good."

  10. #10

    Default Re: buying a used car battery

    new battery with warranty

  11. #11
    Flashaholic
    Join Date
    Aug 2011
    Location
    MD
    Posts
    336

    Default Re: buying a used car battery

    Quote Originally Posted by Mr Happy View Post
    This needs a proper battery load tester that a workshop will have.
    Instead of a carbon pile rheostat you can make a 1 kw load resistor from a length of coiled iron coat hanger wire. It has to be immersed in water during the test.

    In principle, with a body/skin resistance of 300 to 3000 ohms for most people most of the time, 12vdc should give some people a shock [I>1 mA] but I've never felt a thing. The lowest voltage that anyone ever got electrocuted with [in the US Navy] was 47v.

  12. #12
    *Flashaholic* Mr Happy's Avatar
    Join Date
    Nov 2007
    Location
    Southern California
    Posts
    5,390

    Default Re: buying a used car battery

    Quote Originally Posted by xul View Post
    you can make a 1 kw load resistor from a length of coiled iron coat hanger wire
    Only if you know what you are doing. These crazy experiments are all very well, until someone gets hurt.
    Tiefer, tiefer, irgendwo in der Tiefe gibt es ein Licht

  13. #13
    Flashaholic* Russel's Avatar
    Join Date
    Jan 2009
    Location
    California
    Posts
    583

    Default Re: buying a used car battery

    Quote Originally Posted by xul View Post
    [...] The lowest voltage that anyone ever got electrocuted with [in the US Navy] was 47v.
    I remember something about a Sailor killing himself with a Simpson multmeter powered by a 9V battery.

    Resistance is Futile - Darwin Award 1999

  14. #14

    Default Re: buying a used car battery

    I have tested a car battery using a 100 amp load meter and it did not come up bad but when I took it to an auto parts store it was bad and the new battery fixed the issue. I think these big 700+ CCA batteries need about a 300amp load on them to get a decent working check.
    Fenix Split rings 1400+ sent, SWIVELS now available also!
    Psalm 112:4 Light shines in the darkness for the godly. They are generous, compassionate, and righteous.

  15. #15
    Flashaholic* VegasF6's Avatar
    Join Date
    Dec 2007
    Location
    Las Vegas
    Posts
    1,445

    Default Re: buying a used car battery

    Xul you are like some scary crazy MacGyver, LOL.

  16. #16
    Flashaholic
    Join Date
    Aug 2011
    Location
    MD
    Posts
    336

    Default Re: buying a used car battery

    Quote Originally Posted by Russel View Post
    I remember something about a Sailor killing himself with a Simpson multmeter powered by a 9V battery.

    Resistance is Futile - Darwin Award 1999
    In principle 1 joule of energy can be fatal but these defib machines use up to 200 joules.
    To get at least 20 mA with 9v you'd need a skin/body of resistance of 9/.02 = 450 ohms. I guess it's possible, but the effect depends on the current path through the body. Through the chest or head is bad.
    BTW, the elec. chair comes in at ~2400 VAC/~6A = ~400 ohms.

    Regarding
    http://en.wikipedia.org/wiki/MacGyver
    I have found that my ability to rapidly adapt to a given situation has improved by pretending that the problems of each forum poster on many different forums are actually my problems.

    Calculate your risk/benefit ratio, take into account your risk aversion and possible legal liability, don't injure bystanders [because it can turn heros into fools], and go for it!
    Sometimes martial arts training helps.
    Last edited by xul; 11-03-2011 at 10:52 AM.

  17. #17
    Flashaholic
    Join Date
    Mar 2011
    Location
    Germany
    Posts
    233

    Default Re: buying a used car battery

    Quote Originally Posted by degarb View Post
    I need to buy a used car battery, because of cost. ... I know measuring, not voltage, but max amperage a nimh AA can put out is a better indication of health (internal resistance); so, below 1.5 amp max and I can toss it out, as it will refuse to smart charge anyway.

    I would expect a lead acid battery (if comparable to nimh) would put out 24 amps on such a test (12 x 2 amps). My meter goes to 10 amps.

    How to properly test. (testing voltage before and been burned before).
    I would expect up to 1000A depending on the battery. Your multimeter will blow the fuse or it will explode in you hands. If you get a 95Ah AGM battery they all have around 1000A max current.

    Never buy a used car battery. It will maybe work a while but you never know what happened to it before.

    I can give you a free AGM 95Ah or 62Ah battery but you need to pick it up from Germany. Im a car mechanic so I can get the old ones for free and use them for a few years. Those batteries which can be opened are crap. Most times they are dead when discharged too low. Same for the sealed ones which still have liquid acid inside. AGM is the one you want to get. Those are indestructible! Even when discharged under 1V they are still good after charging.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •