[OT] More on Batteries
Bradley Miller
bradmiller at dslonramp.com
Tue May 13 19:30:01 CDT 2003
> > That would make a battery dead in 10 days. I find that hard
> > to believe.
>
>That would be 10% of the 'remaining charge'. i.e.
>
>12V - (12V * 10%) = 10.8V
>10.8V - (10.8V * 10%) = 9.72V
>
>Which means the battery would be effectively dead after 24 days when it has
>less than 1V of charge. Is that believable for some battery types? Maybe.
Actually the voltage on NiCads is like 1.25 (not the full 1.5 of a dry
cell). (There are some "hotter" Nicads that give out a full 1.5, but
we'll leave those out for now.) Going by the voltage rate shown, they
would be down do .91 volts in only 4 days . . . and .9 volts is where
typical discharge cutoff voltage is. (I raced RC cars for years.) Now
instead what the "loss rate per day" is referring to overall
capacity. Take a 1800 mah AA NiMH battery and apply a 10% loss per day on
the overall capacity. The cell may show 1.1-1.2 volts after x days, but
it won't have any capacity (amp hours) left in it.
>However, what about alkaline batteries? I'm looking at some Rayovac's that
>have Dec 2009 written on them. What about lead-acid batteries? I've had
>lead-acid batteries in cars that sat for over 6 months and were still able
>to crank over the engine.
Apples and oranges here. Alkaline batteries are a different beast and
don't have the same loss rate as a rechargeable type battery. The car
battery thing is another "capacity" issue. Most passenger cars provide
very little resistance for a modern battery. Try sticking one of those 6
month batteries in a high compression V8 with a lot of cubic inches. ;-)
-- Bradley Miller
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