On Monday, 9 November 2020 11:31:11 UTC, Martin Brown wrote:
On 09/11/2020 10:19, Scott wrote:
On Sun, 8 Nov 2020 15:25:37 -0800 (PST), tabbypurr wrote:
On Sunday, 8 November 2020 13:42:26 UTC, Scott wrote:

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

There are 2 requirements for a good battery: voltage & current. Terminal voltage often tells enough, but not always. The other test is to touch probes of a 1A meter to the battery for a fraction of a second, see how fast the needle flies up. Digital meters generally can't do this. Keep the probes on & you'll kill both meter & battery.

Given that a humble AA can source 10A into a dead short that would quite
likely wrap the needle round the end stop on an analogue meter or blow
the internal fuse on a modern digital meter.

that's why it's only connected for a fraction of a second. What you're looking for is enough oomph to be confident the needle would fly off the end if it stayed connected. Harmless if not sustained.
You can't use the method with digitals.


Could my battery testing facility (in the multimeter) be doing this?

It probably measures the battery terminal voltage with and without a
suitable load resistor across it.

A load resistor yes, how suitable is another matter. They tend to load them very lightly.


NT