> I looked for an answer in previous discussion but cannot find any. I am
> interested in knowing your advice concerning a minimum voltage for
> rechargeable batteries (to avoid over discharge).
Amandine,
It's an "all depends on" answer as there are so many types and variations of
rechargeable battery available, but I'll hazard an answer.
The old lead-acid batteries are still in widespread use as in cars and
applications such as standby lighting and power backup as in telephone
exchanges and other fail-safe applications but they are toxic and heavy.
they should be stored fully charged.
Nickel-cadmium batteries are more or less phased out now as they had minimum
voltage and reverse charge problems as well as being toxic, like lead-acid.
The battery of choice is now the Lithium-ion type which are reasonably
robust and can stand being self-discharged when not in use, which wrecks
lead-acid types. The recommendation is still to use a custom charger with a
set maximum voltage and current. These are approximately 4.2V per cell
charged and a rapid charge current giving preferably an hour or more charge
time. After that, a good charger should drop to a low trickle charge to
avoid overheating. A hot battery has a problem.
The recommended end voltage is 2V for each cell, but this has to assume the
cells are equal in capacity. If all cells are new, that is easy as an end
point, but a higher end point is advisable on a well-used multi-cell battery
which may have weak cells.
The best advice is to watch the battery voltage or indicator, and when it
begins to drop markedly, play safe and recharge. With a single 3.5v cell,
the end point should be easy to see, but with a well-used multi-cell
battery, the recharge point should be as soon as the total voltage begins to
drop quickly, and well before the weakest cell reverse charges. That's why
they often don't quote an end point voltage.
David Brinicombe
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