Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Testing a battery: is the hygrometer obsolete?

A couple weeks ago my 4 year old WalMart MAXX battery couldn’t turn over the van after I ran a Coleman cooler for about three hours. I easily jump started the vehicle with a small lawn and garden 12V battery I keep in the garage on a trickle charger.

After a couple weeks and some long trips I tested the van’s battery with a hygrometer. I did not read the actual specific gravities, but all the cells read in the red zone (not charged), some slightly in the red zone, some firmly in the red zone.

I drove to WalMart and they tested the battery today. Their device printed out a slip that said GOOD BATTERY; CCA 710 out of the rated 800; Voltage 12.67; Temperature 83 F.

The technician told me there’s no pro-rated warranty after the 3 year free replacement period is up on my May 2012 battery, but that their new batteries are better than mine, and have a 2-year pro-rated warrant after the initial 3 year free replacement period.

He told me they don’t use hygrometers nowadays because there are so many different varieties of plates and acids used in batteries, there would need to be many different hygrometers.

I remain skeptical. Meanwhile I am slow charging the battery and will have more data tomorrow.

Hygrometers, load testers, and carbon piles are obsolete when testing battery’s.

Testing battery’s is now done with a battery conductance tester.

This quickly provides the starting ability of the battery.

But what it doesn’t provide, nor does any other battery test is, the reserve capacity of the battery. This is the amount of the time the battery can provide power without the charging system.

So depending on the electrical load applied to the battery without the charging system, dictates how long the battery can provide power before it’s drawn down.


The last Walmart battery I had lasted a year and they argued about taking it back. It wouldn’t turn the car over even. I bought one of those circuitus or whatever they are called testers that gives you the CCA in relation to the rating and like that. Some say load testing is the only way but I like the quick and easy tester and I can tell on my lawn mower batteries just how much they have deteriorated.

Looks like someone has come out with a battery tester that checks reserve capacity too.


Thanks, Tester and Bing for your replies. I think the battery’s reserve capacity is less than it used to be, if that cooler ran it so far down so quickly. Looking ahead to winter in WI and MN, I think a new battery makes sense.

Is there something to learn (about the condition of the battery, and/or the charging system) from checking the battery’s voltage when the engine is off, then once more with the engine running? What voltages am I looking for?

With the engine off, and the volt meter leads on the battery posts, the reading should be 12.5 volts DC or above.

With the engine running/idling, the reading should be over 13.2 volts DC.


You think a hygrometer is obsolete? Take a look at this:

Does anybody recognize it? Did anybody ever use one? How does it work?

No instructions? No deal. Probably a load tester though for six volt batteries. At least it has green and red zones though. @Triedaq will probably know what it is and how to use it.

@ Bing. I think this cell tester goes back to the days when the cells on the battery were interconnected with metallic conductors on top of the battery. Each cell of s strong battery generates about 2.1 volts. A six volt battery has 3 cells and a 12 volt battery has 6 cells. In these old style batteries, one could bridge across the connectors of a cell and read its voltage. Today’s batteries have these connectors between the cells under the sealed top. In fact, many batteries are sealed so you can’t add water or measure the specific gravity with a hydrometer. I remember when cars began to convert from 6 volt systems to 12 volt systems. I watched a mechanic with a 6 volt powered timing light connect one lead to the positive terminal and the other lead to the output of the middle cell of a 12 volt battery to get 6 volts.

I’ve got a hydrometer or two in one of my boxes but don’t even remember the last time I used them.

Just my 2 cents, but I do NOT trust inductance testers. More than once I’ve had someone at Wal Mart of wherever use an inductance tester and tell me that a known bad beyond all doubt battery is good because of the print out which states “Battery need charging”.
This leads to denial of warranty replacement.
That in turns leads to my sabotaging the battery deliberately to make a point.

For some reason, “The battery has BEEN on the charger and dies on the bench in 2 hours” just doesn’t seem to soak in.
That is usually followed up with "maybe you have a bad (fill in the blank). No, no, hell no. See above statement. And still they argue…

I find a simple Voltmeter works better than anything including finding weak or dead cells.

1 Like

I believe Triedaq has it right. The wavy piece of metal between the two contact prongs is a load resistor. The meter is zero-center so you can make either contact positive – that way, from either side of the battery you can place the tester so that the meter is visible. Clever!

Most batteries are sealed in a way that makes taking an electrolyte sample very difficult. So hydrometers have gone the way of the dinosaur. Not to mention that a larger portion of the population has gone to alternative form factors like AGM for example…

I also do not trust the “algorithms” in these newer tools to be 100% accurate. I bought one of the newer chargers that claimed to be omnipotent about battery condition and it was a royal piece of junk. I returned it and went back to my tried and true, non-digital version…

The tester you referenced uses conductance testing. That measurement is purported to be capable of predicting reserve capacity…

I used the wrong word in my original post: I used the word hygrometer. A hygrometer measures atmospheric humidity.

A hydrometer measures specific gravity. That’s the instrument whose usefulness was in question.

Thanks to all who have responded.

Dang, I made the same mistake! fixed…

A four-year-old battery isn’t worth much diagnosis, I’d just replace it. But in the future, I’d have a charger on hand to make sure the battery is fully charged before testing it, either with a hydrometer or a conductance tester. I use a battery tender to top off the battery, if it’s really low I have an older Craftsman 10 amp charger I use first.

In Texas where it gets ungodly hot - I agree. But in colder weather batteries usually last 7+ years. So it really depends on where you live.

I have had batteries last 7 years here in WI and MN. One battery lost its charge one summer in MT while I was canoeing the Missouri River in 100+F temperatures for a week. A jump got the car started and I bought a new battery as soon as I got home to WI.

BTW I have found MT to be the best place ever to have a flat tire or a dead battery. People there help and they care to do a job right.

I was probably more willing to push the limits of battery life when I was a single man. Reliability isn’t as thrilling as gambling, but has its benefits.

Some version a load test is the best way to determine the battery’s condition. I’ve run into the same problem, modern batteries seem to have a variety of chemistries these days. I guess it’s not accurate to just test the battery chemistry with the hygrometer now, you have to test the ability of the battery to deliver current under load. That’s what they did it appears. When it says

CCA 710 out of the rated 800; Voltage 12.67; Temperature 83 F.

that means under load the battery produced 710 amps at 83 deg F while maintaining a voltage of 12.67 volts. Pretty impressive stats. Compare that to the circuitry in a typical house, where 20 amps is about as high as you’d ever see in an individual circuit.

These testers don’t do a load test, they estimate the CCA.

1 Like