Home battery tester: measures voltage or current?

[Jon D]

I am in the UK. I have a battery tester from years ago which is still available. It may also be sold in the US.

multimeter shows that this battery tester puts a load of 500 mA on the 1.5v battery under test.

I have alkaline, NiCad, and NiMH batteries. I have AA and AAA.

(1) Almost all gets a steady reading of 'GOOD' in green. (2) No battery goes to 'REPLACE RECHARGE' in red. (3) One battery starts in GREEN, then slides into RED over 10 seconds.

Is this tester measuring: (a) the general "health" of the battery (b) the battery's current state of charge?

Presumably (a) could be done crudely by displaying current and (b) by displaying voltage? Is this correct?

[kony]

Yes/no/maybe, you'd have to determine your thresholds for the particular cell technology and size per any rate and charge state, and health is a bad term to use at all.

It will be measuring the voltage even if indirectly but the load is too high, many cells have an internal impedance that will drop the voltage rapidly when trying to deliver 500mA, particularly alkalines far moreso than NiCad or better quality NiMH.

"Health" is not a very applicable term to a battery if only checking the voltage, rather whether it's discharged past the threshold or not. You might hook up a voltmeter in parallel with the tester to see at what threshold the lights turn from green to red.

Perhaps I should now ask, what is your goal, exactly? Analyze this tester? Understand batteries? Test what batteries you have and be done already?

Different battery chemistries can have different voltage curves during discharge. Unless your tester was expressly designed to test NiCad or NiMH, odds are it was mean for alkaline and older battery technologies which tend to drop further in voltage more rapidly, a steeper voltage:discharge curve.

[Bazzer Smith]

Not necessarilly, depends on what you mean.

Yes, basically yes, it's testing if it can deliver the 'correct current', obviously when it is low on charge it won't be able to maintain this for long as in (3) above and will eventually drop into (2).

I am not sure what it says about the rechargability of he batteries though.

Yes as the battery brcoms more 'drained' the measured voltage will drop from say 1.5 V to about 1.0 V. As for 'measuring the current', how are you planning of doing this? If you connect it trough the current terminals of a meter you are short circuiting the battery, not recommended, basically you are 'testing' the battery by draining it. Use the voltage measurement. A multimeter usually has battery testing settings which are simply voltage testing setting adjusted to scales of 1.5V, 9V etc...