testing batteries in cold weather

[Donald]

I have a car battery that is less than 1 year old (but was in a car over the summer/fall that was not driven much at all) and in early winter it did not work well.

I have it on my float charger and its gone into float mode which means the battery is fully charged. I used a 200amp load tester and the battery had a good voltage during a 15 second test.

But I tried an old normal hydrometer and a cheap one (floating balls) and neither gave the battery good marks and seemed inconsistent. But the battery is in unheated garage and is about 32F.

I am assuming the battery is in good shape, but am not positive.

 

[frankiee]

What are the readings of the hydrometer test??
What are the ratings of the battery CCA and RC (cold cranking amps and reserve capacity)
If you can find them marked on the battery.
Some batteries can take a charge but can't hold it for more then a number of hours.
What are the hydrometer readings please?

 

[Eddie]

You are suppose to wait a specific time after charging before hydrometer reading is taken. I don't remember the time though.

 

[Donald]

OK, I will get the hydrometer readings tomorrow. I understand about battery not holding a charge. But if I pull battery off the charger and wait a day or two and redo the load test and it passes, then battery should be OK.

 

[vizvo]

A fully charged cell will show a hydrometer reading of 1.265 at 80° F. You have to adjust the hydrometer reading for temperature. Subtract 0.004 per each 10 degrees below 80° F. Add 0.004 for each 10 degrees above 80° F.

So if the temperature is 30° F, then you have to subtract 0.020 from your measured reading. At 30° F, you would expect the unadjusted hydrometer reading to be 1.285 on a fully charged cell, and after after adjustment 1.265 (1.285 - 0.020 = 1.265).

It is helpful to store the hydrometer in the same room as the battery, so that the hydrometer temperature is the same as the battery temperature. See the Battery FAQ

 

[frankiee]

The reason I like a hydrometer test is that it could foretell future problems.
If the battery is still the way it was designed then the chemicl reaction should be roughly the same in all 6 cells. If active material is falling off the plates or it is starting to sulphate then it will show up in the hydrometer test first and you at least will be forewarned.
On ship I have to check the batteries every week and the cells do vary from week to week. That way I can see the progression of what the cells are doing. Don't scrap a battery if a cell is a bit above or down but watch it.
I know it is a pain to get accurate hydrometer readings but sometimes it is worth it for peace of mind.
By the way: What is this battery starting?
What kind of trouble did you have with it in early winter?

 

[1 FMF]

when you know the battery is fully charged via the float charger, you need to remove the "surface charge" by either putting a specific load on the battery for a certain amount of time or waiting. The preferred method is to just wait, which is at least 24 hours. A car battery should be at 12.65-12.7 volts when at 100% charge. Some battery types might be a little higher like 12.85 volts at 100%. When you take the battery off the charger and measure voltage (even up to 1-2 hours later) you will see 13V or more. Remeasure voltage every 6 hours or whenever practical until it stops dropping, then you can do a hydrometer reading or a load test.

If after waiting 2-3 days the battery voltage drops to below 12.6 volts then you have a bad battery, regardless of any test. Temperature must be accounted for in a hydrometer test and a load test. Best thing to do is get the battery someplace > 60F, especially when charging. Preferably 70-80F when doing any test because if it's cold then that's just a risk and will result in poor test accuracy.

 

[Donald]

OK, tested with two DVMs, one gave it 12.72V and the other 12.6V. Passed the 15 sec load test with 325 amp load.

Tested all cells and they were around 1150. All were in the red section of the hydrometer. They might have been different by 25 points, but no more.

Battery was at 70 degrees or so.

Could I have a bad hydrometer, its probably 10+ years old. I know if you do not pull in enough fluid you get a bad reading (too high).

These tests seem inconsistent.

 

[vizvo]

quote:

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"Could I have a bad hydrometer, it's probably 10+ years old."

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Seems like that is a possibility. Test your hydrometer with distilled water. It should read 1.000 if it is in good order.

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