Inside a Radio Shack 22-032A battery meter

Another handy little meter that I've had for years, so I thought I would take a look at how it ticks. This follows on from my previous comments about multimeters that have battery testing capability and basically there is a difference between the two devices. Testing a battery purely by voltage is not a reflection of the battery health, so it is important to place the battery under load to check. In the case of a battery meter like this one, that is achieved by turning the dial which places an appropriate resistance in the test circuit.

Inside, no battery is needed as the unit uses the tested battery to provide current. I expected to see the calibrated, analog moving coil meter of course and a series of resistors linked to the rotary dial positions, that would be about it I would think, no fancy integrated circuits, just an application of good old fashioned V=IR in a handy little unit, so I took the back off to have a fiddle around. 

As predicted, twelve resistors (for nine dial positions) and annoyingly, some resistors are in backwards in relation to others, so it makes interpreting the bands a little difficult. I checked all the resistors with a multimeter and they were approximately what they should be, within reason. Instead of making a list of the resistors (and their variance from the stripes) I made a table of dial position and resistance recorded at the probe level for both the Neoteck and Klein Tools multimeters.

The dial position selects a resistor, or group of resistors and then the magic of V=IR comes into play for the moving coil meter and full scale deflection if the loaded battery is good, there is some other aspect coming into play for the button cells and AAA and AA cellls, but I was unwilling at this time to remove the meter label or the circuit board to see what jiggery-pokery is happening on the reverse side with the traces and perhaps a couple more resistors, or reuse of one of the twelve. I was tired and I needed a beer and there was also that chance that I would not be able to put it back together again and it would be a battery meter no more.

Suffice to say, clever, yet simple device, it is a shame that Radio Shack no longer exist in the form that they did a decade ago, but there were similar devices branded Micronta in the years that followed their closure and transition into the Source.