Testing small batteries

A voltage measurement in a multimeter measures the tiny current passing through a large resistance. Different resistances for the different scales, but in any case the current is tiny, too small to test the ability of a battery to deliver useful current. My central heating recently started to give problems, so I tested the batteries in the wireless thermostat. According to the multimeter, they were fine, but changing them for new fixed the problem.

A gadget like that should take a higher current through a lower resistance, so would be a better, though not necessarily perfect, test.
 
Cheaper to buy some new batteries?

Primary batteries such as zinc carbon tend to have a tapered discharge characteristic that allows a reasonably useful assessment by open circuit voltage. You have to compare cells of the same manufacturer and type. In a service shop I used to work in we used to test batteries using the 10A range on the old Avometer which gave a good ad-hoc idea of condition.
 
richardabeattie said:
I've been testing AA cells using a digital multimeter on the assumption that if they read anything above 1.4v they're still usable. Would I do better to use one of these?

https://www.connevans.co.uk/product/993840/MX690402/Universal-battery-tester-with-LCD-readout
Click to expand...

I used to do the same as you but accepted a lower figure for batteries to be used in devices that drew very little current. eg clocks

I now have a multimeter with a couple of battery test ranges, 1.5 and 9 volt, that measure the volts while drawing a small current. 20mA and 5 mA respectively. Interpretation of the results is still down to me though.
 
richardabeattie said:
I've been testing AA cells using a digital multimeter on the assumption that if they read anything above 1.4v they're still usable. Would I do better to use one of these?

https://www.connevans.co.uk/product/993840/MX690402/Universal-battery-tester-with-LCD-readout
Click to expand...

Some multimeters have a battery test function for 1.5 volt batteries, sometimes 9V and 12V as well. This puts a load across the battery and gives a more accurate reading.

What you're doing is near enough, looking for an open circuit voltage over 1.4V
 
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I also use a multimeter with a battery test facility and find that some things dont stop working till below 1 volt,also use rechargeable batteries which are 1.2/1.3 volts fully charged.
 
It might seem horribly crude and cruel but simply put a multimeter on 10 amp range across the cell. This measures the max current it can supply or is an indication of internal resistance. (being high when cell is dead) You only make the connection for 1 second or so but will quickly indicate good or bad. AA cells can usually give around 1 or 2 amps but will give no current if dead even if they measure 1.3 volts or so. olewill
 
William_H said:
It might seem horribly crude and cruel but simply put a multimeter on 10 amp range across the cell. This measures the max current it can supply or is an indication of internal resistance. (being high when cell is dead) You only make the connection for 1 second or so but will quickly indicate good or bad. AA cells can usually give around 1 or 2 amps but will give no current if dead even if they measure 1.3 volts or so. olewill
Click to expand...

What he said...If it can produce both Volts and Amps then it's a good-un!

P.S. Don't accidentally try this with a lead-acid battery, by forgetting to switch your multimeter range, and also don't ask me how I know to warn people of this danger !
 
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