1.5V batteries - AA - when are they "done"?

I think that's the reason. Modern electronic test meters have very high resistance so they don't load the battery. If you are able to measure the voltage across the appliance terminals (with the battery in place and the appliance turned on) you may find it's lower.

I had a similar experience with a PP9 9 V battery in a smoke alarm which was giving a low-battery chirp at about 6 AM each day (when the house is coldest and so the chemical reaction in the battery is at its slowest). With a high-resistance voltmeter it was reading 8.5 V, but when I replaced it with a new battery (9.2 V, no load) it was fine. Unfortunately the terminals were not easy to access once the battery was in place, so I couldn't measure the voltage when the battery was under load.

They often do that.

I have a tester for that: a small single-cell flashlight, with an old-fashioned edison-style non-LED glowing-wire bulb. Tired cells (and tired Nicads) show up in a few tens of seconds -- the light dims. (Not much else use for it now that there's good LED flashlights.)

Thomas Prufer

As others have said, a DVM has a very high resistance so only draws a tiny current when measuring voltage on the 'voltage' setting. Some DVMs have a 'battery voltage' setting, where the DVM actually draws some current while the voltage is measured, so more typical of 'in use' conditions.

I test my used AA cells by seeing what current they will supply when connected to my DVM set to the 10A range. Typically 4 to 5 Amps for a new Alkaline cell, but <0.5A for one that is 'dead'. It's no more than a

Or test the voltage using a tester with a load suitable for the battery. I have an ancient Tandy one that I must have had for 40 years. It has separate settings for AA and AAA

Save apparently "dead" AAs for small LED torches, these will drag every last electron out of them.

David explained on 27/04/2020 :

Yes, nail head!

Thomas Prufer expressed precisely :

Some LED flashlights can 'suck' the last dregs of power from an otherwise dead cell. They use an inverter, to boost the voltage to a usable voltage.

Or make a joule thief!

Any appliance needs enough voltage AND enough current. A cell can fail on either one, or both.

NT

It depends upon the electronics in the device

my old Blood pressure monitor ate up batteries because of the pump inside.

It showed batteries as expired as soon as they got to 1.5v each

I could then put these same batteries into less demanding devices and get another 6 months use out of them

tim

The measurement of a battery is meaningless its the internal resistance which is key. IE as a battery is used up part of the electrode area becomes less efficient, so a given current drain will drop the voltage over the increasing internal resistance due to the smaller area of electrode working. This is why you have to measure under load.

Now is it possible to reverse this decay? Well partially. Some chargers that can handle multiple types of cell can charge so called rechargeable Alkaline. These can only be charged if you only use them for a while, then charge them, then use them. The closer to flat you go the worse the results are. If you are brave, however the chemistry inside rechargable alkaline is exactly the same as in your normal alkaline. The only difference is that the seals are better, and I have got good results charging alkaline that are normal types. However some do leak and the stuff that comes out tends to corrode metal, so on your own head be it. OK for a cheap torch, but don't use them in anything worth any money!

Brian

Mine's the same and the bloody thing uses AAA cells. It can store data but that flattens the cells rather quickly and, to add insult, the data are lost when the cells are removed! Solution is to take out the cells between uses. It warns against using rechargeable cells, I assume due to the high current and low internal resistance of such cells - the pump relies on high resistabce to limit the current that it can draw. Cheap and nasty (and inconsistent).

In the days of Uher portable tape recorders, TVCentre sound Mtce ahd a box labelled "Used U2s", fine for many things, but not good enough to take out in a Uher.

So saying, can't say I've ever seen a primary cell which reads 1.5v off load but won't work where it is meant to. Would be a pretty rare fault. And two doing the same even rarer.

First thing I'd do is make sure the connections to the batteries are clean,

With radio mics, we'd generally replace the batteries at the beginning of the day, and again for dress rehearsal. (rather than just before the TX, to make sure not a duff new one)

Complete overkill, as with the twin PP3 Microns, decent batteries had a life of about 50 hours use.

I had a pile of them last year. Nothing rare about it.

yep

NT

You bought a load of duff cells? Hope you learned your lesson. ;-)

of course not.

Yep, I learnt that recharging dry cells sometimes works, sometimes doesn't.

Not sure you've learnt anything.