Car Battery Load Test Results (Is this good or bad?)

[pally]

Hey everyone I appreciate your help,

First I will explain how I performed my load test, then I will ask for your professional opinion what these results mean for the cars battery, thanks!



1st) I tested the voltage with regular voltage test and results were 12.0V on the dot

2nd) I tested the battery using the "load test" setting on my multimeter and it read 11.7V

Based on the above can we assume the battery is good or bad?




Finally if I test the current of the battery running through the car while it is turned off to check for a current leak, what is a typical amount to expect while the car is off for amps running through?


Thanks again!

 

[shrtrnd]

I'm not a professional with car electrical systems, maybe one will input info in a following post.
I can just tell you what I do.
Put your voltmeter across the battery, which will probably read 12V just fine, then, while
watching the voltmeter, turn the starter, to start the car. If you drop to 8 or 9 volts while
the starter is turning (a genuine load test), your battery is bad. If you stay around
12 volts you're probably ok. (If your starter isn't bad)
Otherwise there are a lot of possibilities for a current leak through all the electronics in
cars these days. (Which is what it sounds like you're looking for). But the only one
I've found of obvious significance is when you blow a diode in the alternator, and it allows
a constant draining of your battery when the car is off.
I don't know where you're at. In the U.S., most auto supply stores will check all of the
above items at no charge. Battery, Starter, Alternator. If they're all good, THEN you
can look for a current leak elsewhere in your electronics.
That's my 2 cents worth.

 

[pally]

I'm not a professional with car electrical systems, maybe one will input info in a following post.
I can just tell you what I do.
Put your voltmeter across the battery, which will probably read 12V just fine, then, while
watching the voltmeter, turn the starter, to start the car. If you drop to 8 or 9 volts while
the starter is turning (a genuine load test), your battery is bad. If you stay around
12 volts you're probably ok. (If your starter isn't bad)
Otherwise there are a lot of possibilities for a current leak through all the electronics in
cars these days. (Which is what it sounds like you're looking for). But the only one
I've found of obvious significance is when you blow a diode in the alternator, and it allows
a constant draining of your battery when the car is off.
I don't know where you're at. In the U.S., most auto supply stores will check all of the
above items at no charge. Battery, Starter, Alternator. If they're all good, THEN you
can look for a current leak elsewhere in your electronics.
That's my 2 cents worth.

I actually saw two seperate things listed on the web,

one said if a load test of a car battery is 9.6V then the battery is completely dead so getting close to that means your car battery is shot.

second I saw people saying the a 12V battery that reads 12.6V on an open voltage test would be a sign it is 100% charged, while an open voltage test of 11.9V is a battery with 25% charge.


I can find plenty of sources explaining how to conduct a load test with a multimeter that has a load test setting, yet none of them tell you what the results mean LOL, I know for a fact that a healthy 12V battery should read 12.6 on an open volt test, but how low is too low etc?


thanks

 

[eKretz]

I am pretty sure there isn't a multimeter made that will be able to properly load test a 12V LA car battery. A proper (most reliable) load test is half the rated cold cranking amps for 10 seconds. There are special load testers made just for this purpose (carbon piles for the loads). Shrtrnd's test is a good shade-tree mechanic check too, as long as you prevent the car from starting right away (remove fuel pump fuse or similar). All cars are different as far as power-off current draw. On top of that, most newer cars have power-cut systems that will cut off parasitic draws to unnecessary components when the car has been off and undisturbed for a certain period of time. Some of these can draw as little as 25mA when "asleep." To check for a parasitic draw I usually pull one fuse at a time and just put my leads into the fuse terminals to check each circuit's current draw individually.

 

[shrtrnd]

Unless somebody put one on the market that I don't know about, eKretz said what I
think. Relying on a DVM for a load test is not workable.
At rest, a lot of bad batteries will read 12V. You NEED to load it to test it, and turning
the starter is the easiest one I know of. I'm still waiting to see if somebody else comes on here
with a reliable different way to load test, than just having an auto-parts store put it on
their testing machine.
Maybe a little more information might help point you in the best direction to go with this?
The alternator could be bad, not recharging correctly.
The starter could be going bad, dragging mechanically and over-taxing the battery.
Are you having a problem starting, or believe you're experiencing a power-drain overnight,
or what are the symptoms that you're experiencing.
CAN, you take the vehicle to a place nearby that does a free check of your electrical
system, with equipment designed for that purpose?

 

[pally]

Unless somebody put one on the market that I don't know about, eKretz said what I
think. Relying on a DVM for a load test is not workable.
At rest, a lot of bad batteries will read 12V. You NEED to load it to test it, and turning
the starter is the easiest one I know of. I'm still waiting to see if somebody else comes on here
with a reliable different way to load test, than just having an auto-parts store put it on
their testing machine.
Maybe a little more information might help point you in the best direction to go with this?
The alternator could be bad, not recharging correctly.
The starter could be going bad, dragging mechanically and over-taxing the battery.
Are you having a problem starting, or believe you're experiencing a power-drain overnight,
or what are the symptoms that you're experiencing.
CAN, you take the vehicle to a place nearby that does a free check of your electrical
system, with equipment designed for that purpose?

I load tested it the way that you guys mentioned, I was just driving the car so the battery was at 12.4V off, did load test by having friend start the car and it dropped off to 9.6V exactly when starting at its lowest voltage.

The car was tested by a professional and I know it failed the test, overall I'm just trying to learn how to do this for fun.

 

[duke37]

9.6V at the battery seems reasonable to me. It could be much lower at the starter due to poor connections and wire resistance. Make sure that the engine is properly bonded to the chassis.

 

[shrtrnd]

duke37 has a point. The absolute first thing I do before I try testing the electrical parts
on my car is to clean the battery contacts (and cable terminals connected to them).
Corrosion formed from the battery acid fumes can cause bad battery contact.
I see duke37's point that bad electrical contacts or corroded wiring would lower the
battery voltage at the accessory receiving the voltage (cause a V meter directly onto
the battery contacts would read the full voltage), but I wouldn't trust a battery reading
9.6 volts when starting. I think it's about to die. (But that's just my opinion).

 

[duke37]

It all depends on the vehicle. I used to have a Sunbeam Rapier, the batteries only lasted a couple of years. My used batteries went to my sister's Austin A35 and lasted many more years.
My brother had a Ford diesel which was a terrible starter. The local garage replaced the thin cable from engine to chassis with a much thicker cable and there was no more trouble.