ehsjr said:
The problem most certainly *is* that cells may be damaged.
See "Discharge Termination" in the Energizer
Battery Application Manual, pages 14 - 16.
http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf
Ed
Thanks for the interesting reference, Ed.
I see that you were referring to a potential situation involving
series-connected cells in which one or more cells caused a voltage
reversal on one or more of the other cells. This could cause damage to
the reversed voltage cell.
Good point, and thanks for the correction.
I still would argue, of course, that such a consideration is one of many
that would enter into a full-blown project design that involves numerous
tradeoffs. While the "cure" is to ensure that the total voltage remains
above 0.9 volts/cell x number of cells, there is a real cost to doing
so. And what is the expected benefit from this precaution?
Unfortunately, that information is not given in the reference. "May"
cause damage is not sufficient information to evaluate the
cost-effectiveness of a fix. "May" could well range from a probability
of 0.01 to 0.99. Even if the probability is near 1.0, the extent or
nature of the "damage" is unstated. Does the damage mean catastrophic
component failure? Does it mean a 10% reduction in capacity (truly a
form of damage) or a 90% reduction?
Charge and discharge rates are further examples of tradeoffs involving
possible damage and costs.
I would repeat that the purpose of this project is surely not the
preservation of the batteries. It is to accomplish some other purpose.
Whether the inconvenience of more frequent battery charges would offset
the benefit of reduced (but unknown) risk of battery damage (of unknown
consequence) is a design decision. Good engineering practice REQUIRES
that such tradeoffs be considered, but it does not require that
batteries be made free of risk of damage, although that is always an
option.
Having said all of that with much huffing and puffing, I must admit that
a possibly more conservative "battery low" criterion is probably a
pretty costless step and a good suggestion, Ed.
Chuck