What determines if a car battery is still good?

Question

Reading the specs on my battery it says 12V - 36AH /5HR

(?) What does the 36AH/5HR mean?

If I were to compare the following 3 batteries

Battery A

Brand: Acme

Model: 1234

Specs: 12V - 36AH/5HR

This battery is functioning properly and just came back from a 8 HR car trip

Battery B

Brand: Acme

Model: 1234

Specs: 12V - 36AH/5HR

This battery has been working fine, but the lights were left on over night, now the battery is dead.

Battery C

Brand: Acme

Model: 1234

Specs: 12V - 36AH/5HR

This battery is no longer working and needs to be replaced.

If you took all three batteries into sears and they hooked them up to a machine to test...

1) What is the machine testing?

2) The battery that no longer works, what happens to it? No longer puts out 12Volts or no longer puts out enough amps?

I just bought a sears multimeter that measures ac/dc voltage/current / resistance / termperature / capacitance/frequency / continutity/diode test. Can I test my battery with this

Answer 1

Load test is the only assured way to determine a battery goodness. A ok way was to measure the density of the acid in each cell. This could tell you if the battery life is less than 50% .

Most batteries are designed for 60months, after that you are on borrowed time.

A battery loses its CCA (cold cranking amps) by about half for every 10degF below freezing. It typically takes 250 - 350 CCA to start a car engine. At 20deg F the capacity of a 650CCA battery is down to about 400CCA. That's why weak batteries can't perform when old and in cold weather.

As the lead within the battery gets a sulfate coating on the plates inside the ampacity capability is reduced. The lead chemically reacts to the acid to produce electricty and the result is a lead sulfate. Eventually all the plates are used up. Sometimes a quick blow, Be Extreemly Carefull, to the side of a battery can bring a little extra life back to get a engine started, but this is short lived.

Never Ever use a Marine battery to start a car. These are designed for slow discharge, where as a car battery is designed for hard discharge and recharge.

A typical car battery puts out 12.6V and is charged when the engine is running usually at 14V - 14.6V. A charging system at 16V can damage a battery and should be corrected, usually the regulator within the alternator has failed. Use of a DMM can detect this.

Car batteries give off Hydrogen gas, very explosive, especially during the charging process, even the sealed versions.

So it was good you have a multimeter, but that's not enough to determine the goodness of a car battery. Have the battery and charging system checked out at a local car parts store, usually they'll do this at no Charge!   ha ha that was a funny

However, some multimeters can check the goodness of your dry cell batteries, AA - D pretty well.

Answer 2

Wow.. thats alot. You could try looking it up on google or ask.com those are some really good and popular recources! Good Luck! :)

Answer 3

Every battery has got a life.The difference of these three batteries are the manufacturing date of the battery if they have the same manufacturing date than you have to check the recharge unit and charging unit belt which is connected to the motor.For every battery you have to check all conditions of the batteries,heat ,geological conditions, manufacturing date,maintenance card if ok.It hasn't got anything to do with the resistance and so on.But the life of car batteries are for normal conditions is 3-4 years after this period nothing will helps.In the other hand if you have got some extra installed lights ,CD players, air conditioners ( the accessories which is not originally on the car) shortens the life of the batteries.

Answer 4

"fil Yerboots" gave a good general answer, but there is a bit more to your issue than what has been thus far said.

First of all, the 36A/H generally means that the battery will supply 36 amps for 1 hour, until it is dead, or 3.6 amps for 10 hours. The 5HR, generally refers to the reserve capacity of the battery.  Battery A, yes, and ??? Most batteries fir into that condition because the alternator was recharging the battery as it should, and is part of the function of the alternator. Battery B is also a normal condition because the owner forgot to make sure all electrical switches were properly turned off. This would also be a normal condition.

Battery C is either at the end of it's useful life, or has been poorly taken care of.

To really check your battery, you need a charger analyzer made by Vector Manufacturing Ltd. Their toll free number for service issues is 866-584-5504. Calling this number should enable you to find out where to buy one. It is an excellent unit, well worth the cost. It does an excellent job of testing, cycling the battery, that is, discharge and recharge, as well as changing the battery condition in terms of sulfur sulfate removal from the battery plates. This sulfur sulfate kills a battery, but it can be removed, to some degree by a charger built to do that job.

Most bad batteries have a cell that has shorted, thus rendering the battery unusable. The plates can also become sulfated to the point that battery chemistry can no longer produce a voltage. This is the main reason why a battery may look "good" in that it seems to have a good charge because a meter reads 12 volts, but it can not support a load,

Answer 5

The test done by Sears etc is commonly called a drop test and the battery must be fully charged (or have been "on charge" for sufficient time and current that it should be). The drop test puts a very heavy load on the battery. Depending on the size of the battery, the operator should know how long it should still keep its voltage for. Most places do the test for free because they know that if it fails the test, it wont restart your vehicle and you will have to buy a new battery from them.

Its best not to do drop tests too often as it will itself deterioate the battery.

You cannot do this load test with a multimeter but you can use it to determine another couple of important things on your vehicle that may tell you everything else is good if you are having battery problems.

Measure the voltage of the battery with the engine stopped. You will get around 12v. Start the engine, it should got up to around 14v. This shows the alternator is charging.

Switch off everything in the vehicle. Disconnect one battery connection, making sure there is no spark as you do this as a spark would indicate there is a load that is running your battery dead. Connect the meter on dc amps between the battery terminal and the conection you removed. You should have no current flow showing nothing is running the battery dead. Be careful with the meter when its on amps because you don't want to connect it across the battery.

Answer 6

The machine places a load across the battery and measures how much the volt drop is. The battery can be also be tested for charge holding by measuring the rate at which the power drops off. All you can do with your multimeter is see what it has in it under no load. The real testing needs a bank of resistors to give a much more realistic scenario