Specific gravity and how it effects a battery

At the John Deere Tractor shop, we have a used tractor that when another store took it on trade, they filled a couple of new batteries and threw them in the tractor without charging them. (Most Deere batteries are shipped dry and filled at the store when you buy them.)

The tractor hasn't been cranking over fast enough so I was checking the batteries. First up was the Multi-meter. 12.5 volts or so on each battery, but I never trust a multimeter on a battery. I then load tested the batteries with a 120Amp load tester. This actually showed them to be good, but I was still uncertain since it wasn't much of a load for an 8D battery.

Out with the multimeter again and I checked the voltage between each cell and had right about 2.2 volts each. Well, I wasn't sure about this, so I asked the boss man and he grabbed his specific gravity tester.

I sampled each cell and they were all just above being water. The lowest number on the guage is 1100 with 1200 being the lowest part of "fair" and 1300 being fully charged. My readings were about 1125.

Unfortunately this meant that the salesman was probably right. (of course he knew more of the story than we did, so I'll let him have that one)

So I put the batteries on little trickle chargers at 2 Amps and after half a day they showed no improvement, so I got out the bigger, 10 Amp charger and hooked it up to one battery. This battery started to bubble and give off that rotten egg smell we all know and love.

I checked the SG of the cells about every hour and it slowly came up and up, bit by bit. Tomorrow, I'll start it charging first thing in the AM and see if we can get a full charge on it by the end of the day.

My reason for posting this is because I have read Gurus post that you should check specific gravity, but it never really hit home until this occurred.

The battery passed two voltage tests, and it passed a load test, but it didn't pass the specific gravity test. If you are having slow starting problems and the battery reads 12 volts, that doesn't mean that it is fully charged. Get a specific gravity tester (AKA Hydrometer or refractometer) and check the specific gravity of each cell.

Here is a website that goes into much more detail about batteries and how to test them. I want to include this link since I am far from an expert and it's important to get information from more than one source when reading on the internet.

Here is the first site I went to that has one kind of tester.

Here is one more link, this one to a refractometer.

**Post location disclaimer**

I guess I'll post this here in TDI 101. This post is a bit of general information that applies to all cars, TDIs as well as non-TDIs. VW and Toyota's, Dodges and Deere. I can't find a best place for this post since it is so general, so I'll just post it here in TDI 101. Forgive me if it's wrong.

Whitedog,

The original battery in my 2000 Jetta finally bit the dust back in October. On the multi-meter it shows about 12.45 volts, but on cold mornings it was showing that its life was over.

I never done any of the other tests. But, considering the battery was manufactered in 1999 there was not much doubt its life was over. So, as you said, passing the multi-meter test doesn't mean its a good battery.

I use 12 volt transformers (300 to 800 miliamps) to rejuvinate batteries that don't get much use (tractor, boat, trolling motor, etc.). It can take up to a week to bring a battery back to life.

Andy

Since it's a sales tractor, they may want to warrantyt he batteries. That would mean that I would take them out and put them on our battery jumper cart after charging them for a week or so. I'm curious about the trickle charger though and why it wasn't showing any improvement and why it wasn't bubbling and smelling.

Perhaps the plates were so covered that they couldn't allow sufficient charge through to the fluid? WAG, but doggies should understand that.

Sulfation in new batteries? I just don't know. I thought hat was a long term thing, but I'm shakey on specifics (no pun intended)

Maybe they did put just water in the dry batteries instead of battery acid.

It could happen, but I'm optimistic that they are smart enough not to do that. But new parts guys are hired all the time, so it's possible.

Would battery acid SG drop that low if worked too hard without ever having been charged up?

High amp/voltage would cause close to distilled water to bubble, but without the sulphur smell. If they have the acid in there, and they were dry to start with, wouldn't they have a coating on the lead? You may need the extra "umph" to get through the PbO(2) (guessing on the number of "O's"). I suspect the battery's were on the shelf for quite a while.

They may have been on the shelf, but they would have been dry. It is my understanding (which may be wrong) that batteries don't suffer any ill effects from dry storage.

Look at a piece of lead - scratch it - and look again in a few minutes. There is something that happens, and I'm just WAGGING here - after wine -

whitedog said:

The battery passed two voltage tests, and it passed a load test, but it didn't pass the specific gravity test. If you are having slow starting problems and the battery reads 12 volts, that doesn't mean that it is fully charged. Get a specific gravity tester (AKA Hydrometer or refractometer) and check the specific gravity of each cell.

Click to expand...

Well, if you have a 12V battery and it shows 12V when measured without a load then it IS discharged. A FULLY charged (and I mean a fully charged, not many chargers will actually fully charge a battery) would show over 13V when measured without a load. Actually it will show approx. 15V when measured shortly after the charger is disconnected (or just below is more correct).

There is many handy tools out there, but you have to know how to operate them to get any use of them. Even if I agree with you, to measure the SG is a way more accurate way to say something about the status of the battery.

So now I have a question for smart people. If it takes 18 hours to charge a 1300 CCA battery, does that mean that it's no good?

Dog,

What was the SG value? That will tell you the approximate % of sulfuric acid. This thread is a good reminder to check electrolyte.


conc sulfuric1.84

whitedog said:

So now I have a question for smart people. If it takes 18 hours to charge a 1300 CCA battery, does that mean that it's no good?

Click to expand...

It's impossible to tell from the information you give.

Yup. CCA is nothing to do with Ah.

Airliner said:

It's impossible to tell from the information you give.

Click to expand...

It's impossible for me give you the information if you don't tell me what information you need.

nicklockard said:

Dog,

What was the SG value? That will tell you the approximate % of sulfuric acid. This thread is a good reminder to check electrolyte.


conc sulfuric1.84

Click to expand...

Due to time constraints, I ended up with one battery at 1275 and one battery at 1250 average. All cells were within 20 of each other.

DPM said:

Yup. CCA is nothing to do with Ah.

Click to expand...

I'll check the Ah today.

Dry Batteries

In one of my past lives, I worked in automotive battery design and testing. Dry charge batteries used to be a big business, but eventually our company quit making dry charge batteries for the automotive market. Dry charge batteries were fully charged like any other lead-acid battery. The electrolyte was dumped from the battery, the battery rinsed off, and then air dried. It was then sealed and placed in inventory somewhere.

You had to completely charge the battery in order to form the negative and positive battery plates before you dumped out the charging electrolyte. A dry battery is then activated at the point of sale by pouring electrolyte back into the battery. Technically, at this point the battery should be at a high state of charge. The battery self discharge rate in the "dry" state is low since there is no electrolyte in it.

Frankly, I don't understand why the specific gravity would be low in a dry battery that has just been activated. After all, sulfuric acid and water combination is poured in the battery, not water. What did these guys pour in the batteries? They did not use water, did they?

All lead-acid batteries have an electrolyte that is around a 34% concentration of sulfuric acid in water. It will vary a little based on the size of the battery with small batteries generally having slightly higher gravities. Batteries use this acid concentration because it has the highest electrical conductivity and the lowest freeze point.

Despite what has been said on the forum, there is a general correlation between AH capacity and CCA (cold crank amps). It is true that glass-mat gas recombinant and gel electrolyte batteries have a lower ratio of CCA to amp-hours because they are electrolyte starved. But that is for another discussion.

Dick_Larimore said:

All lead-acid batteries have an electrolyte that is around a 34% concentration of sulfuric acid in water. It will vary a little based on the size of the battery with small batteries generally having slightly higher gravities. Batteries use this acid concentration because it has the highest electrical conductivity and the lowest freeze point.

Click to expand...

34% Sulfuric acid concentration yields a specific gravity of 1.44 grams/mL.


WD, that's what the individual cell's SG value should be near. I'm not sure what units you were reporting before...mg/mL? If so then you want 1440 per cell or near to. Also if those were the units you were working with, it means the acid concentration is at 29.5% average.

{derived: 1.88*X%conc.sulfuric + (1-X%conc.sulfuric)*1.00 = 1.26| X =.26/.88 = 29.5%}

Dick, thanks for your knowledgable reply. When it comes to sparks, I know I can count on you for the stratight poop. What I failed to mention was that the batteries were filled, tossed in the tractor and the tractor sat for a few months with a small draw somewhere.

I have been wondering about our batteries because customers would come to the counter, wait for it to be filled, then walk out without it ever being on the charger. It makes sense now with your explaination.

So does the long charge cycle mean anything about the condition of the battery?

Nick, you are working in a different field and I think that there is some discrepancy with the numbers. Take alook at that first link I gave in the first post. It has the 1.275 type numbers that are a standard in the automotive battery industry.

Oh, okay...couldn't find any units on any of the links though...hmmm a unitless quantity for specific gravity...could be refractive index or angle of refraction....weird way to do it though. *Nick hates non-standard unitless numbers!*

Anyhow, according to your first link:



So according to your first and fourth posts, you got them out of the severly discharged range and up to snuff on one, and nearly so on the other 3.

nicklockard said:

hmmm a unitless quantity for specific gravity

Click to expand...

Specific gravity is unitless by definition, since it is the ratio of the density of one substance (battery acid, in this case) to the density of a reference substance (water).

SG = DensityOfStuff/DensityReference

The units of density (g/cm^3, slugs/foot^3, what-have-you) cancel out and you're left with a unitless number.

SG is also referred to as "relative density" which is a bit more descriptive.

scurvy

*boinks head*

I was thinking plain old density. Right you are.

I would not be too concerned about the long charge time. However, a battery that has sat around a long time with a parasitic drain likely formed a lot of lead suflate on the plates. Lead sulfate crystals lock up what was active lead in an inactive state that does not contribute to any chemical to electrical conversion. I own one of the Battery Minder chargers that can supposedly break down lead sulfate given time. It would be interesting to try one of those charges on this battery.

I just went out and checked the SG of the 2.5 Y/O battery in the Jetta and all cells rear about 1.150 which is the top of the "recharge" zone. Once I can park my car closer to the garage, I'll put it on the charger over night.