Performed a battery load test tonight

[ltslimjim]

So, I have a very basic load tester I got from Harbor Freight the other day. I let the car sit for at least 3 hours after sundown and hooked up the tester. It read at about 12.6V. I engaged the actual load and the voltage dropped to around 10 and stayed there. I only held the load for about 5 or 6 seconds, but it didn't raise nor did it fall, however. It also didn't go really far down and then raise to 10. Translation, marginal battery?

After load testing twice, for no more than 7 or 8 seconds at most, the voltage at the battery without load read at around 12.3 or so volts.

The car still starts etc, but come this summer this may leave me stranded or what? It's the little Civic so IDK, maybe this is causing the alternator to put back too much and I risk needing an alternator($150+) vs. a battery($75 @ Costco)?

I've heard 9 or lower with a load test is a 'bad' battery.

Thoughts or advice is appreciated. Thank you.

 

[Lead Shoes]

The battery in my Civic was about 10 years old and read 9 volts right after turning off the car and testing it, it still started my car in 0 degree weather, but it was iffy and just barely got the car to turn over so I replaced it when I found 70 dollars I didn't need.

 

[ag_ghost]

Really basic, but it's familiar from a class I took last year:
http://autorepair.about.com/library/weekly/aa101604c.htm

 

[Chris142]

How many amps does the load tester put on the battery? If the battery is supposed to be load tested at say 200 amps and your testing it at 300 amps it's going to read as a weak battery.

 

[ComfyShorts]

Rule of thumb is that load test amperage = 1/3 of battery CCA.

 

[LargeCarManX2]

Run er till she dies....

 

[ltslimjim]

Originally Posted By: Chris142
How many amps does the load tester put on the battery? If the battery is supposed to be load tested at say 200 amps and your testing it at 300 amps it's going to read as a weak battery.


I used this tester here:

http://www.harborfreight.com/100-amp-6-volt-12-volt-battery-load-tester-90636.html

I have a 51 battery currently. The car is supposed to have 51R, but this is from the PO. I got the car at the end of 2009. This is a 2008 dated battery, IIRC.

It was probably around 65 degrees. I did not know about the relative to CCA information.

This load tester supposedly is a set 100 Amp tester. This battery CCA capacity when new is supposed to be either 475 or 465. I had it tested last summer at an Interstate Battery location and the test measured about 410 CCA at the 85 degrees it was that day or so. Voltage at the battery was okay, will try to find it. With the car on, it read around 14.2V at the battery from the charging system.

So, with only 100 Amps for 5 or 6 seconds it could only hold at 10 V or so today. The initial reading pre-test was 12.6 V, however after the 1st test it recovered to just below that, etc.

Seems marginal, but not necessarily terrible yet.

EDIT: I believe the factory service manual calls for 410 CCA for these Civics.

 

[ltslimjim]

Originally Posted By: ag_ghost
Really basic, but it's familiar from a class I took last year:
http://autorepair.about.com/library/weekly/aa101604c.htm



Hmm, on the last page of those series of pages, about reverse polarity.

What would that do to the car's electrical system?

I left the headlights on for a 'measureable' amount of time since owning the vehicle on this same battery.

The first time, about an hour or so. Slow charged the battery, this was during the summer of 2010. Topped off the cells with distilled water; especially nearest the posts/terminals. I think the negative side was really low compared to the positive, but both posts were 'low'.

Then, 1 year ago(spring of 2011), I left the headlights on for 3 hours. Needless to say, the car wouldn't start without a jump at this point. The year before, it still started. So, after the jump and driving home(15 miles or so), I charged the battery over night. I believe the fluid was topped off again within a month. Now, fast forward to today another year forward.

I suppose what would really help is a DVOM.

 

[Texan4Life]

yeah the instructions for the tester are vague. The steps on the volt meter of 200 - 1000 are CCA ratings. so if you have a 400 CCA battery with the 100 amp load it should read at the 400 step mark or higher.


I think that is how it works.

 

[Vikas]

DVOM are cheap (under $20) and you can pick up one at Sears.

 

[ltslimjim]

Okay, that's awesome b/c I've been finding high pricing on some DVOM at auto stores and the budget is 'very' tight. Thanks.

Found some at their site, will check local stores. Also, wouldn't you know it Amazon has some as well.

 

[mechtech2]

How about another approach?
If the resting V and running V is OK, then you are good to go.

 

[Vikas]

For DVOM, if you have HF nearby, you might be able to find a coupon for free one. I picked up couple of them last year. I compared them to a Fluke at my work and I found the HF one matching the voltage reading from the Fluke!

 

[Donald]

You should have gotten the carbon pile one from HF. You need to put a load of 1/2 the CCA for 15 seconds (its beeps) and read the voltage on the temp compensated scale to determine the health of the battery. I would assume the load should be there for 15 seconds even with the tester you got.

 

[Tegger]

Originally Posted By: ltslimjim
So, I have a very basic load tester I got from Harbor Freight the other day.

Waste of money and time. You're better off with a standard digital multimeter (DVOM).

To check the battery properly, KEY OUT OF THE IGNITION:
1) turn headlights ON, and wait five minutes;
2) turn headlights OFF again, then wait another five minutes;
3) check across the battery terminals with your DVOM.

If you see ANYTHING less than 12.65V (even 12.64V), the battery is at least partially discharged.

Now, with the engine COLD, start the engine.

With
the engine RUNNING, but COLD,
A/C ON, headlights ON, and rear-defroster ON,
check across the battery terminals with your DVOM. You should find no less than 13.5V. If you find 12.65V or less, the system is not charging.

Your car has an Electrical Load Detector (ELD). This thing can cause a lot of confusion, since it makes it more difficult to make sure the charging system is actually charging.

If the system IS charging but the battery still presents less than 12.65V in the first test, then it cannot hold a charge and is need of replacement.

 

[ahoier]

Originally Posted By: LargeCarManX2
Run er till she dies....
Yep. As long as all the cells look level....if they aren't just top them off with distilled water, and run it til it dies....

If you're afraid of the inevitable.......keep a set of jumper cables in the car with ya

The cheapest pair you can buy should be able to jump that

 

[ltslimjim]

@mechtech2, that's a great idea. I am new to the electrical game more so than other areas even. Thanks for the tip. Now to get reliable equipment.

@Vikas, I'll see what they have. Couldn't hurt for a starter, since it's a trial/learning process more than anything for me right now.

@Donald, Ah I see what you are saying regarding different tools. In another theory, I only put a 'small' load on the battery for a few seconds(this device says not to load test for more than 10 seconds, and gives cooldown time...yeah, it's cheap. So, if a smaller than 1/2 CCA load brought the Voltage down to 10 immediately, what does that mean?

@Tegger, Last summer an Interstate Battery location tested the voltage at the battery with the vehicle running, it was around 14.1-14.2V. After immediately testing with the vehicle off, their tool showed 13.4V at the battery(it was 123 degree F either in the engine bay or at battery itself, their machine was measuring the temp somehow). I do have pretty lame idle symptoms when there is more electrical load or amp draw during the day(no headlights running), like when the A/C cycles on or the radiator fan/cooling fan come on. I'm also having IACV issues too, without a CEL. It is a 'slow' 20 year old vehicle.

I believe the battery is probably still fine, but needs to have the fluid checked.

 

[mechtech2]

Tegger - Yes but....
Temperature [ambient] is important to battery V readings. This must be addressed.
And to do that running test, it should NOT be at idle - rev it to 1,500-2,000 RPM.

 

[ltslimjim]

^True. I guess I do need a decent DVOM then and report back later.

I'm just trying to learn right now. I'm not looking to replace and waste just for the sake of it.

The idle voltage vs voltage with engine load(2,000 rpm or so?), with electrical components turned on including that rear defogger with it's larger amp draw, correct?

I've been wanting to get a DVOM to perform a voltage drop check anyway.

 

[Donald]

A hydrometer is always a good method to test a battery if the caps come off. If you add any distilled water, you must drive it around for a day or two to mix things up before doing any testing.

Good info on battery voltage
http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

Also remember the battery gets a surface charge after being charged and you either need to turn on headlights for 5 minutes or let it sit for 24 hours not connected before you measure the voltage. You need an accurate voltmeter. Maybe not a $200 Fluke but not the free one from HF either.

Best to fully charge with an AC charger to take very accurate battery voltage measurements. And wait for the surface charge.

Some measurements for peak current or minimum voltage taken during cranking require either a Midtronics battery tester or a scope. The peak function on a normal voltmeter is just not fast enough. Even an inexpensive scope is 25Mhz meaning it is doing the measurement 25 million times/second.