This electronics tip has to deal with checking common alkaline AA/AAA batteries or AA/AAA rechargeable batteries for proper voltage with a voltmeter.
Disclaimer : some people might say that a battery should always be tested under load but I have found that in most common household applications this is insignificant and will not change the results of the testing too much.
Things that you will need :
+ Alkaline battery
Basic facts :
The proper voltage for AA/AAA alkaline battery is 1.5V
The proper voltage for AA/AAA NiCd/NiMh rechargeable battery is 1.25 Volts
To test the battery, turn on your voltmeter, put the voltmeter on DCV and make sure that it is far above the battery voltage, on most voltmeters there is a setting "20" in the DCV area, so switch your voltmeter to that setting.
With the battery in front of you, put the red probe to battery's nipple (+) and the black probe to the battery's flat side (-). Notice the voltage reading on the voltmeter.
If the reading is more than 1.3V for alkaline battery (not rechargeable battery) then the battery still has some juice left in it, don't throw it away. Otherwise, properly discard of the battery.
Tip : do not use old and new batteries in the same device at the same time. Try to use batteries that have same amount of energy stored in them.
Another tip: I sort my batteries according to Voltages, 1.35+ Good, 1.2V-1.3V Ok (but almost out), 1V-1.2V Discard.
I will attach some pictures of measurements in action.
Instructions on how to use a multimeter are out of scope of this Instructable, you can find some information here: http://www.ladyada.net/learn/multimeter/