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.
What happens to the voltage of that battery when it does that ?
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.
Not even possible with the NiCad and NiMH batterys with something that cheap.
To be certain.
Not feasible to work that out with alkaline, NiCad and NiMH batterys.
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.
Nope, its actually displaying the voltage under load.
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.
