[OT] More on Batteries

[Zscoundrel]

Bradley Miller wrote:

>
>> > 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
>
>
>
The actual loss rate for ni-cads is about 1 percent.  
(I think it was something like .93 or .89% - but the actual number 
escapes me right now.)

Ni-cads can be twitchy beasts , they usually do have a lower voltage 
level than other batteries for typical physical sizes, they operate a 
full output levels for almost as long as most battery types and then 
'tail off' dramatically where other battery types voltage levels tend to 
fade away slowly.