Battery testing

[Telegram Sam]

Layman's question: I have now become the proud owner of a digital multimeter which can also test batteries when the owner remembers where to turn the dial to. If I test a new 1.5V AA / AAA battery the reading is around 1.3. Is there a generally accepted cut-off point below at which it is wise to replace the battery? Or is it a case of how long is a piece of string, sorry wire?
Tks.

 

[Marvo]

The digital multimeter doesn't put the battery under any load whilst it's being tested so what you're seeing is the no-load voltage which isn't really a very good indicator of the health of the battery. You'd be much better using one of these .

 

[Engineer54]

While you're at it, also buy a budget Anologue multimeter, as the majority those digital multimeters will not discriminate between normal and phantom voltages.

 

[Telegram Sam]

Very interesting -> that (avoiding phantom voltages) is precisely what I had in mind. I've got one just like the pic you sent which failed years ago, also a much smaller version (again with a needle dial) with just green, yellow and red segments (which has yet to fail). Until you destroyed my illusions I was assuming that the digital was more accurate. Are you saying that all the ones with needles / analogues test the no-load voltage, or do you have to discriminate?

 

[Lucien Nunes]

1.3V is not correct for a new AA cell (other than a rechargeable) unless you are a long way below zero degrees. A new alkaline is normally about 1.56V at room temp, 1.3 is fairly low, some equipment stops working around 1.1V P/C. Different chemistries (e.g. cheap zinc chloride batts) give different voltages. Also, their 'wear-out' mechanism is not just falling voltage but rising resistance, which you can't effectively test with a multimeter. NiMH and NiCd Rechargeables have a nominal 1.2V P/C, which varies very little between full and empty. These are also hard to test with a multimeter unless you know their history of what the voltage usually is at a given state of charge.

 

[Telegram Sam]

Sounds like compromises are necessary, or continue in a state of ignorance! Is then the least worst option to get hold of an (any?) analogue meter and take the results as a no-load approximation? And replace the battery when the needle moves out of the green zone.

 

[HandySparks]

The digital multimeter doesn't put the battery under any load ....

If your multimeter has specific battery test positions on the function select dial, it means that the meter will apply a small load, which will provide a more useful test than an off-load one. One of mine has settings for 1.5, 9 and 12V.

 

[Telegram Sam]

My meter is pretty basic and I don't think it has this feature, going by the Chinese instructions, just the different voltage settings. Is this something only to be found on the more sophisticated meters? Which is yours?

 

[HandySparks]

My meter is pretty basic and I don't think it has this feature, going by the Chinese instructions, just the different voltage settings. Is this something only to be found on the more sophisticated meters? Which is yours?

Not really specific to 'sophisticated' meters. Some have the feature, some don't. The 'professional' meters won't; it's just a convenient thing to have for the general domestic/householder user. Saves having to pick a suitable resistor and needing three hands to apply test leads and load resistor at the same time.