Originally posted by glanglois my NiMH Energizers and Eneloops charge up to about 1.4V. By 1.2V they're so far down that they're hard to charge. They spend most of their time between 1.38 and 1.28V.
Open circuit voltages (ie: with no load) would be about the same for Energizer 2500mAh NiMH and eneloops - because they are both basically NiMH batteries.
However under load - like being used - their behavior can be significantly different for voltage sensitive devices - like Pentax dSLRs (that use AA batteries)
For example the K100D would shutdown when the voltage drops below 1.19V each (= 4x 1.19V = 4.76V) - eneloops manage to maintain voltage level better than the Energizer 2500mAh -
I am borrowing SilverFox's excellent discharge graph of the Energizer 2500mAh NiMH
If we look first at the 2Amp discharge curve (dark green) we can see that after about 0.4Amp-hours (on the horizontal axis) the curve has dropped to abut 1.19V - the cut-off voltage of the Pentax K100D -
So if the K100D drew 2Amp constant current (which it doesn't) - then at 0.4Amp-hours which would be about 0.2 hours or 12 minutes the K100D would shutdown because the batteries would not be able to deliver enough current at the required voltage - or saying the same thing another way for the required current of 2Amps the batteries are no longer able to maintain a voltage above 1.19V - both are saying the same thing - but to be strict - it is the battery unable to deliver the required power - watts......
Now look at the 1Amp curve (mauve/burgundy) it manages to stay above 1.19V until about 1.6Amp-hours - at 1Amp this would be about 1.6hours.
So at a lower 1Amp draw the batteries would last about 1.6hours (if it was contant current - again this is not really the case - but just a mere example) -
At the lower current of 1Amp one can see the K100D could utilize more of the battery's charge of about 1.6Ah out of a tested total 2.230Ah - whereas at 2Amps only about 0.4Ah is utilized out of the tested total of 2.236Ah.
Now let's look at the eneloop - discharge graph again borrowed from SilverFox -
Using the same 2Amp draw curve (dark green) one sees for the eneloop - the curve does not dip to 1.19V until about 1.4Ah.
And for 1Amp (mauve/burgundy) the curve stays above 1.19V until about 1.7Ah.
So the eneloop manages 1.4Ah out of a tested total of 1.807Ah at 2Amps,
and 1.7Ah out of a tested total of 1.871Ah at 1Amp......
The respective total energy tested were -
Energizer 2500mAh NiMH
2.555Wh at 2Amps
2.674Wh at 1Amp
Eneloop
2.158Wh at 2Amps
2.320Wh at 1Amp
clearly the Energizer 2500mAh NiMH hold more charge/energy than the eneloop -
Yet the eneloop would be able to deliver more of its charge/energy than the Energizer.