Do you jump it by connecting to the negative post, or to some metal part of the car? it may well be that you have dirt on the ground where it connects to the body, and there’s enough space in there to collect moisture and freeze, so you have a ring of ice on cold days. Clean the connector, and the place where the ground connects, and maybe get a new bolt.
Getting new wires wouldn’t hurt either, in case the insulation is loose, and you are getting moisture inside, which freezes, plus has caused some corrosion.
You can just try this and see what happens, or you can test it, by waiting until the next time it won’t start, and then trying to jump it by attaching the cable to the negative post on your battery, and if it won’t jump, then attaching it to the body, and seeing if it will jump that way. If it does, the problem is the ground wire or connection-- which probably means the battery isn’t recharging well either. If the ground wire isn’t good, the positive wire probably should be replace as well.
OTOH, cleaning the ground connection can’t hurt, and costs nothing, so unless it’s in a really awkward place, you might just as well go ahead and do that.
I take it this is an automatic, so push starts are not possible.
::: sigh::: I took all that time to write out how to check the resistance of the cables , and you ignore it and do an ohm check.
Here is why you can’t test the resistance with an ohm meter
Let’s suppose you starter will draw 200A when the engine is cold (a reasonable number)
Let’s also suppose you positive has 0.02 ohms resistance. You can’t measure that level of resistance with an ohm meter.
So let’s do a little ohm’s law shall we?
200A X 0.02ohm = 4 Volt drop in the positive cable
That means if you put 12.6V into the cable you will only get 8.6V at the starter. And the car won’t start.
Now how about you test the cables the way I told you, and you can get your car fixed. Or you can continue to fuck around with tests that don’t work. Or take it to a professional who will charge you $ to do the exact test I told you how to do for free.
Your call.
::: shrug:::
You still could do the voltage drop test on the negative cable, instead of doing the correct test you chose to do a worthless test.
As far as the positive cable goes take it to someone who can diagnose it and happily pay the money because it appears this repair is beyond your ability.
Even if I could tell with 100% certainty the cable was bad since you can’t access it to test it, I doubt you will be able to change it. In this case I think you will be ahead of the game to take it to a shop.
What I don’t understand in all of this is why the new battery appears not to be able to hold a charge. I just retested it and it is at 12.3V but tested as a good battery when the auto parts store tested it.
Should a battery at 12.3V be able to start a care in 20F-30F degree weather?
Is it possible all of this is a bad battery despite what the part store claims?
What temp was the battery when it was in the store and what temp was the battery when you measured the 12.3V?
The chemical reaction in the battery slows down as the battery gets colder, thus less available voltage. So if the battery was 70F at the store and 20F after the battery has sat all night and you measured it, that would be normal.
To answer your question yes it is possible for a bad battery to test good but with modern testers assuming the battery is profiled correctly it is extremely unlikely.
Assuming the cables are good (I have some serious doubts about the condition of yours) yes 12.3V will start the car.
In the store and in the car? About 50-60F. When it didn’t start I put my voltmeter on immediately so it did not sit in cold temperature and it read 12.2V. After sitting out all night and being at about 0F overnight and 25F this morning it read 11.85V.
Also, I got it back from the shop charged at 12.75V and upon install and first try to start (click) it immediately dropped to 12.25V and stayed there. She put in 790 CCA into the tester but of course it doesn’t say the actual CCA - just that it is good.
Wait, what? Before you said the battery had 960 cold cranking amps, now you are telling me the tested it @ 790?
That is totally wrong. If the batter is a 960 cold cranking amp battery it has to be tested as a 960 CCA battery.
Go look at the battery. What EXACTLY does it say on the label?
Does it say:
960 Cold Cranking Amps
Or does it say
960 Cranking Amps?
If it is the latter look in the small print for a CCA rating.
No. Essentially it’s doing manually what the starter motor does electro-mechanically – rotating the crankshaft as it normally sits. Generally a mechanic doing this just judges the effort required by feel. Getting a meaningful reading from a torque wrench ranges from difficult to impossible, as does finding useful information about what such a reading should be.
I double checked before the last post
960 CA @ 32F
790 CCA @ 0F
But the lady (she wasn’t sure how to use the battery testing machine) put in the the correct CCA but told me that she “told the machine” to test at 30F. Not sure what the hell that means.
Get another car and jumper it. Get car #2 and jump with it also. Engines off. Add a battery charger that will put out 50 AMPS & add that to the supply…
Now it will turn or burn. If it burns, look at where the smoke is coming out and there is your problem.
IMO the biggest problem is the emblem. “Jeep” Nuff said…
12.76V as carried in, or after being charged at the store? 12.76V having stabilized over time, or very soon after being taken off a charger? 12.76V and 12.26V measured with the same voltmeter? 12.76V before load testing, and then neither charged nor tested again until put back in the car?
Something there doesn’t make sense – a normal good battery doesn’t lose half a volt being carried from the store to the car.
Temperature has a very minor affect on rest voltage – according to the chart you can find here (click on “Temperature Compensated Battery State-of-Charge (SoC) Tables”), less than 0.1 volt difference between 70ºF and 30ºF. Also note that according to the chart, the 11.85V you mentioned before is essentially a dead battery.
Whatever other issues the car may have, the battery voltage readings you’ve supplied indicate a problem with the battery. If that’s the case, you’re not going to get anywhere until that problem is resolved.
Double check your check list of things to check.
First check is battery condition and rating, you say yours meets the cars specks.
Next check would be the voltage drop test at all the points where you might loose voltage. I don’t believe you did this. If the car were hard to crank the voltage would have dropped below 11.7 when you were trying to crank it. Connect the negative of your volt meter to the block and try it there. If you can’t reach the starter then take it to the shop. You have to check everything or you are simply guessing.
