On 12/11/2020 00:55, Paul wrote:
Fredxx wrote:
On 11/11/2020 03:13:29, wrote:
On Tuesday, 10 November 2020 11:10:41 UTC, FredxxÂ* wrote:
On 10/11/2020 03:04:36, tabbypurr wrote:
On Monday, 9 November 2020 10:16:51 UTC, Martin BrownÂ* wrote:
On 08/11/2020 13:59, Fredxx wrote:
On 08/11/2020 13:42:21, Scott wrote:

My multimeter has a battery test facility that shows the
battery as good or bad (or on the margin).Â* I understand a zinc
carbon battery has a voltage of 1.5 Volts and an alkaline
battery has a voltage of 1.2 Volts?Â* How does it know the
difference between a very good alkaline battery and a very bad
zinc carbon battery?.

An alkaline battery also has a nominal o/c voltage of 1.5V

A good fresh alkaline can be as high as 1.6v open circuit.

They start off above 1.5v. 1.5v is only nominal.

A well used one can go as high as 1.8v under odd circumstances. I had
a couple do that earlier this year. They were well used then
recharged, and gave a strangely high output. No idea why, none of the
others did.

Most articles suggest a brand new alkaline battery starts at 1.65V o/c
and goes down from there.

Do you have reference you can cite for a well used one with a o/c
voltage of 1.8V?

no, haven't looked.

I have and 1.65 is the highest I saw for a new battery. An old battery
will typically be 1V.

The only odd circumstance I can think of will be a duff meter.

I told you what the circumstances were. The meter's fine. But feel
free to get stupid again.

Perhaps it was user error then, or not recognising a malfunctioning
meter?

If you have any non "stupid" reason for the erroneous measurement,
please do let us know.

Have we no electrochemists in the house ?

https://michaelbluejay.com/batteries/rechargeable.html

Â*Â* "NiZn's have the highest initial voltage of any rechargeable AA or
Â*Â*Â* AAA battery.Â* The nominal voltage is 1.65, and fresh out of the
Â*Â*Â* charger the voltage is as high as 1.85V."

https://en.wikipedia.org/wiki/Nickel...93zinc_battery

Â* (ˆ’) electrode:€ƒ Zn + 4 OHˆ’ ‡Œ Zn(OH)42ˆ’ + 2eˆ’ (E0 = ˆ’1.2 V/SHE )

Â* (+) electrode:€ƒ 2 NiO(OH) + 2 H2O + 2 eˆ’ ‡Œ 2 Ni(OH)2 + 2 OHˆ’ (E0 =
+0.50 V/SHE)

It's a redox reaction with two half-cell potentials, that give
the overall battery cell output voltage.

Was this battery mixed in with a lot of other batteries ?

Well spotted!

The 1.8v muppet was talking about *rechargeable* alkaline batteries when
everyone else was discussing single use primary alkaline AA batteries.

https://en.wikipedia.org/wiki/Alkaline_battery#Voltage

You can briefly see higher terminal voltages for a rechargeable battery
still under charge or very recently taken off a fast charger.

I have never seen a battery whose voltage increased significantly with
use as its remaining capacity decreased. YMMV
(but I expect that it doesn't)

--
Regards,
Martin Brown