battery capacity

[Wills]

Hi all,
I am using lithium thionyl chloride batteries. I want to know how much
of charge is left in it after some usage of a 5 hours. How can I find.


Thanks and regards,
S.Muthuraman.

 

[Gareth]

On 26/03/2011 10:40, Wills wrote:

Hi all,
I am using lithium thionyl chloride batteries. I want to know how much
of charge is left in it after some usage of a 5 hours. How can I find.


Thanks and regards,
S.Muthuraman.

The datasheet for the battery should give the capacity, usually measured
in Amp Hours (Ah) or milli Amp hours (mAh).

If you know how much current you are drawing for the five hours you can
work out how many Ah you have used by multiplying the current in Amps by
the time in hours.

Assuming you started with a new battery, subtract that from the original
value given on the datasheet and that should give you the approximate
remaining capacity. I say approximate because it depends on when you
consider the battery to be completely discharged and at what current
drain it is measured.

For example if you only draw 1uA from a 1Ah battery it probably won't
last 1000000 hours because the battery's self discharge is going to be a
lot more than 1uA. Similarly if you try to draw a very high current the
voltage drop across battery's internal resistance will make it appear
flat even though it may still be capable of powering a lower current device.