CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

Testing a battery: is the hygrometer obsolete?

If the estimate is an accurate one, that’s the same thing as a load test.

It might be accurate, just saying it didn’t put the battery under load.

1 Like

Load testing may be out of style but it works and leaves no doubt about the results.

3 Likes

We began using the hand held battery conductance testers 20 years ago. It can be difficult to get a “failed” result with this type of tester, sometimes the battery must sit for 4 hours.

The Midtronics GR8 battery test station we use now uses a combination of load testing, charging and conductance testing. The testing is automated, it can take up to two hours for a test to be completed.

Back in the good old days, we had an ammeter gauge in the car. It was great for monitoring the electrical system. If the ammeter read high for an extended period of time, I would get out my trusty $1.98 hydrometer that I bought at the discount store. It had four or five floating balls of different densities. The more balls that were floating meant a higher charge in the cell. This hydrometer was useful in isolating a weak cell. When I got a little bit ahead on my fiances, I spent another $1.98 and bought a hydrometer of the same type to test the freezing point of the coolant on the radiator. Since batteries are now sealed, my way of checking the battery is to have my wife crank the engine while I put the probes of the voltmeter across the battery and monitor the voltage drop.,. When rhe engine starts, I can get an idea of the alternator output. I didn’t use a voltmeter on the old days because you couldn’t go to a discount store and buy a voltmeter for $10 as you can today.

I’d rather have an oil pressure gauge or ammeter… And get rid of the tachometer. But people want a tachometer. I guess it makes them think they’re going faster.

@MikeInNH. I’m with you on this one. My Dad explained the meaning od the gauges to me when I was a curious 10 year old. On one family vacation in a 1949 Dodge, I noticed that the ammeter was at the top of the scale. My Dad said that he would check it out the next day. As it turned out, the car wouldn’t even start the next morning–the battery was too depleted to even light the head lights. The battery had a shorted cell even though the battery was only a year old. On the next vacation, I noticed that the oil pressure gauge was fluctuating all over its scale. I called it to my Dad’s attention. He immediately pulled off the highway into a parking lot for a little store. He and I walked to a station about a mile away and came back with 2 quarts of oil. That didn’t get the dipstick up to the full mark, but we drove to the station and bought a third quart. Now, if as a 6th grader I understood what the gauges meant, there is no excuse for a person old enough for a driver’s license not to know. John Rosamond who has a syndicated column once a week on parenting did not think a “smart” car such a new Chevrolet Malibu was the right car for a new teenage driver. His message was that the smarter the car, the dumber the driver and the dumber the car, the smarter the driver. My first car which I bought when I graduated from college in 1962 was a 1947 Pontiac. It was a dumb car with many things wrong with it, but with my knowledge of machinery and a little common sense, I made the 350 mile trip to graduate school without problems. I like a safe, reliable car, and I think part of being safe on the highway is some understanding of how a car functions.

I have to ask… How do you sabotage it?

I almost got to that point once on a new car I had. It was 6 months old and the factory battery started getting corrosion around the positive post. I took it in under warranty and the service advisor told me that was not covered because cleaning the post was “Maintenance”

I went back and forth and ended up giving up the fight. I thought about making the battery fail somehow. I never did.

A driveway diy’er can get a pretty good estimate of the battery condition doing a simple load test themselves, needing nothing more than a volt meter. Just use the headlights as the test load. Hook the meter up to the battery, and note the voltage first thing in the morning, before the car has been used. For a new battery it will be something like 12.5 volts, varies a little w/ambient temperature. Then – continue to leave the engine turned off – turn on the headlights to high beam. If there’s something else that draws a lot of current in a repeatable way, turn that on too, like the heater fan and rear window defroster for example. Now check the battery voltage again. For a new, properly charged battery it will read something like 12.0 to 12.2 volts. The difference between the first reading and the second (usually around 0.4 volts) is a measure of the battery condition. The bigger the difference, the worse the battery condition. Keep a log book of these readings, and the ambient temperature. If possible, start doing this at the time a new battery is installed. You’ll be able to easily monitor the battery condition on a monthly basis. No need for no fancy load tests. I keep two sets of measurements, the battery voltage at the posts, and also at the connectors. That provides me a measure of how tight and clean the connectors are to the battery posts too.

Tester