Home battery tester: measures voltage or current?

  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.

http://www.avenuesupplies.co.uk/getimage.php?id=98&type=1&format=2

My 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?

 

Wont load here.
http://www.avenuesupplies.co.uk/index.php?id=602&pid=98&sid=1
does tho.


Not ever, even when flat ?


What happens to the voltage of that battery when it does that ?


Not even possible with the NiCad and NiMH batterys with something that cheap.


Not feasible to work that out with alkaline, NiCad and NiMH batterys.


Nope, its actually displaying the voltage under load.

  On Thu, 6 Jul 2006 16:02:19 +1000, "Rod Speed"


  They place a fixed load, and test for voltage.  The problem is that
with the batteries the world has been using, the charge/discharge
curve is a long straight line right up until it avalanches with a
pretty quick slew to near zero volts.

  I'll bet that repeat tests will have the cycle occur more quickly
each time.  That battery is likely near discharge.


  The meter is reading the voltage through a fixed load, so I'd say
it's the voltage that is dropping.  When removed from the load,
certain batteries "bounce back" a bit.  This is only by voltage, and
it will again fall under loaded tests, eventually yielding no further
rebounds of significance.


  To be certain.


  Loaded testing has always puzzled me with batteries, as they are
limited fill storage devices.  Upon a loaded test, I find myself
wanting to "top off" the battery again.  Also, as you stated,
performing such tests doesn't really reveal charge level.
  At the rates modern batteries are slow charged, the best solution to
one's unknown battery condition is to "top 'em off". In other words,
put them back in the charger and let its built in detection routine
decide the battery's fill level.  Those "watchdog" chips are pretty
cool stuff.


  Yep.

  For charge rate, and or fill level, one would have to know the
physical characteristics of the battery under test.

  It's fully charged internal resistance, and it's internal resistance
right at the discharge avalanche point, and its very nearly fully
discharged internal resistance.  With this knowledge, one can test a
battery while it is being charged at a known fixed current limited
rate.  It can be determined by knowing the at rest fully charged cell
voltage, and comparing it to the voltage required to get the battery
to take charge at any given point during a charge cycle (not including
fully charged of course).

  With these chargers being current limited, what takes place is that
the voltage is just above that required to pump electrons into the
battery.  Any more and the charge rate current would be exceeded.

  So, a dead battery impresses a very small voltage, or emf when near
dead.  Hook up a smart charger, and it will raise its voltage until it
just starts to pump current into the battery, it will bring it up to
the current limit rate and slowly raise the voltage as the battery
charges up keeping said current rate steady as she goes.  At some
point near the end of the charge cycle the chip is programmed to
provide, the voltage of the battery will no longer continue to rise
and the current will begin to fall off.  The chip will sense this and
change the charge indicator to green and discontinue charging
operations.  Usually, in chargers, there is a chip for each battery.
I have even seen batteries themselves with them built in. Particularly
when there is an array, or true "battery" of cells arranged, and
designers want to insure that all cells get charged evenly and fully.
Memory effect got shot in da head.

 

What I said below.


Its nothing like near zero, and that is why I asked
if it never shows red even when the battery is flat.


Which is why I asked if the others ever show red.


Yes, but its rather surprising that only one battery ever does that.


It shouldnt. Its pretty pointless just measuring
the unloaded voltage with many battery types.


You dont normally leave it on the tester for long.


Sure, but that 'tester' is clearly a very crude approach to battery testing.


Not feasible with a simple cheap tester like that one tho.


Sure, but thats an entirely separate matter
to what that cheap battery tester can do.

 On Thu, 6 Jul 2006 18:55:32 +1000, "Rod Speed"


  The activity doesn't puzzle me, the logic does.

 Even a loaded test doesn't tell one a battery is full.  It can only
tell one something if one witnesses the battery in its death throws.

  So to me, it is pointless at any point during a battery's life as
the thing is LIMITED, why take more away from a fixed amount?

  A simple voltage test, and knowledge of the battery tells a lot.  If
it is a 1.2 or a 1.5 volt battery, and you are reading that or even a
bit more, you know the dang thing is charged.

  I have seen NiCads in particular discharge with an incremental drop
in voltage through the cycle.  I can tell when it is charged too.  I
was using an HP lab supply with a 4.5 digit meter on it and very
precise constant current or constant voltage modes.

  Really all one needs is a good meter and a lab supply.  Read the
battery voltage.  Set the supply to just over that, say a half a tenth
of a volt to start. Set the current limit on the supply to the battery
maker's spec. Place the battery on the supply, and read voltage with
the handheld, reading current on the supply meter.  If the power
supply is set to the battery spec charged voltage, and there is no
current flow, it is charged.  Turn up the voltage to see the current
rise up to the limit point, and read the supply voltage.  It should
not be much more than the correctly charged battery voltage is.

  Remove battery from charger, and let it sit for a few minutes to let
its internal thermals re-homogenize.  Read battery voltage with meter.
Make a report that has each battery's serial number and fully charged
and settled battery voltage (we should really be saying "cell" Replace
the word "battery" with "cell" throughout this post).   Do that with
all of your CELLS.  Any time you want to know a CELL'S condition, read
its voltage, and refer to the chart. The closer it is to that value,
the closer to fully charged it is.  The increment is very small.

 One could also find out the rate the battery is, and discharge what
would be half that, and take readings on each battery, and log the
value.  Then one could extrapolate charge level from voltage reading
fairly well.  They avalanche late in their duty cycle, but the line
from the beginning to the avalanche point is a smooth, slow, small
decline over a couple tenths of a volt.  Meter needs to read
hundredths at least.