Testing Batteries With a Multimeter

DoctorIz

According to Radio Shack (http://www.radioshack.com/uc/index.j...tteries05.html)

How to test batteries

The most important thing to understand about testing batteries is that batteries will not show their correct voltage unless they are under a load. If you simply take a multimeter and connect the leads to each battery terminal, you will not get an accurate reading.

Battery testers are designed to place the battery under a load in order to get an accurate reading and are best for normal consumer use; however, multimeters provide a more accurate reading of the voltage potential. If you are needing a high level of accuracy (such as for design or testing), then you should use a multimeter. If you are just wanting a device to let you plug in a battery and know whether or not it's still good, a battery tester is a better choice.

When testing batteries with a multimeter, you must have the meter set to measure DC voltage and place the battery under load by using a resistor in parallel with the test leads of the meter. If the voltage reads the same on a multimeter with the resistor or without, then the battery is either low or dead and should be replaced.

A battery can be used until it is down to about 30% capacity. After that, it typically will not supply enough voltage to power the product in which it's being used. The actual cut-off voltage will vary.

DoctorIz

Duracell says:

They also provide a graph that can be used to tell how fresh your battery is and how long you can expect it to last. Worth checking out.

http://www1.duracell.com/oem/primary...alkvoltage.asp

a7ecorsair

I've read through this entire thread and agree with much of it as far as testing, the series resistance of the battery, and the use of various testers. The idea of reverse charging a dry cell battery with another in series is a little far fetched.
Kent, OP, in this clock mentioned above, how did you determine that only one battery was dead or weak? If the clock has two separate circuits then yes, only one may be bad.
Batteries in series, like a two cell flashlight, with discharge evenly assuming there isn't some other issue with one of the batteries. Weak batteries will have a low voltage when measured with a multimeter. When a 1.5 volt standard battery, i.e. AA, C, D and the like, measure 1.2 volts, it is pretty much dead. Some equipment won't work when the open circuit voltage of a battery is less than 1.3 v. Button batteries come in several voltage levels so their application will dictate what is the cutoff level.
When a flash light battery gets weak the light just gets dimmer and dimmer, but with electronic circuits, the device just quits working.
Use your multimeter to test batteries. The more you use it to test various batteries the better feel you will get for what is good and what needs replacing.