Chris wrote: said:
Hi, Mike. When consumer batteries are rated for A-h (amp-hours), they
are typically given a constant load, and are considered dead when the
output voltage reaches 60% of specified voltage (in the case of a 9V
transistor battery, that would be 5.4V)
Of course, any battery is _really_ dead by the time it reaches 60% of
rated voltage. I'd consider a 9V battery with a 25mA load very dead by
the time it got to 7V or so. Once the output voltage slides below 80%
of nominal, it's got one foot in the grave.
I just got a look at:
http://data.energizer.com/PDFs/522.pdf
Looks to me there is a bit of a "knee" in the discharge curve with the
"center of the knee" at 7 to 7.2 volts (1.1667-1.2 volts per cell), but
the "knee" only stands out a little. With intermittent duty and a
constant resistance load, the time to 5V is about 50% longer than the time
to 7V.
The constant current discharge curves show mAH about or slightly more
than 7/6 as great when discharged to 4.8 volts as at discharge to 6 volts.
Meanwhile, as for what voltage to design something to work at with this
battery? Since the datasheet has constant resistance and constant current
hours-to-specified voltage curves (as a function of resistance or current)
only for 6 and 4.8 volts, I would design something using this battery to
keep working at least until the voltage decreases to 6 volts.
Although I think it's OK for a product using this battery to work but
not quite meet its specifications below 7.2 volts, I believe that a
product designed to use this battery should work reasonably at least down
to 6 volts.
Meanwhile, in general design of products using alkaline batteries: I
believe they need to work well with NiCd and NiMH that are typically 1.2
volts per cell, and considered discharged at 1.1 volts per cell *or less*.
So I believe a product needs to work well at 1.1 volts per cell.
- Don Klipstein (
[email protected])