Button battery life ruined by shorts?

[Geoff C]

Hi all,

Having received the other day a barebones PC with CMOS amnesia and
discovering a marginal backup battery, this occured to me: It is quite easy
for many types of button battery to suffer temporary shorts when being
inserted into battery compartments because of the closeness of the +ve and
-ve contacts. I am thinking of watches, gameboys, calulators etc. I expect
mercury, silver oxide and lithium will have different properties here.

Does anyone have a good feel for the quantity of damage to the useful life
of a new battery when subject to such shorts? Maybe the high internal
resistance stops excessive damage?

 

[David L. Jones]

Geoff C <notinterestedin@spa.comm> wrote in message news:<waENc.21177$%r.232567@nasal.pacific.net.au>...

Hi all,

Having received the other day a barebones PC with CMOS amnesia and
discovering a marginal backup battery, this occured to me: It is quite easy
for many types of button battery to suffer temporary shorts when being
inserted into battery compartments because of the closeness of the +ve and
-ve contacts. I am thinking of watches, gameboys, calulators etc. I expect
mercury, silver oxide and lithium will have different properties here.

Does anyone have a good feel for the quantity of damage to the useful life
of a new battery when subject to such shorts? Maybe the high internal
resistance stops excessive damage?

From memory the internal resistance of the lithium button cells is in
the order of 20ohms or something like that, so it's reasonably low.
Not sure of the other technologies.
So you'd certainly loose a fair perecentage of your capacity if you
shorted it out, and it is indeed easy to short these little things
out.
I'm aways careful when inserting them, especially into long use items
like watches.
I take care when handling them too. If you put grotty hands all over
them it's not hard to leave some grime behind which can cause leakage.
With some devices having up to 10 years battery life these days,
losing any capacity at all by shorting or leakage could mean losing a
year or more of life.

Dave

 

[Franc Zabkar]

On 29 Jul 2004 03:23:54 -0700, tronnort@yahoo.com (David L. Jones) put
finger to keyboard and composed:

Geoff C <notinterestedin@spa.comm> wrote in message news:<waENc.21177$%r.232567@nasal.pacific.net.au>...
Hi all,

Having received the other day a barebones PC with CMOS amnesia and
discovering a marginal backup battery, this occured to me: It is quite easy
for many types of button battery to suffer temporary shorts when being
inserted into battery compartments because of the closeness of the +ve and
-ve contacts. I am thinking of watches, gameboys, calulators etc. I expect
mercury, silver oxide and lithium will have different properties here.

Does anyone have a good feel for the quantity of damage to the useful life
of a new battery when subject to such shorts? Maybe the high internal
resistance stops excessive damage?

See this datasheet:
http://data.energizer.com/datasheets/library/primary/lithium_coin/cr2032.pdf

The internal resistance is about 35 ohms, and the capacity is about
200mAh.

By my reckoning, if you short the battery, then it will supply up to
100mA. Now 100mAs = 100 /3600 mAh = 0.03mAh, which is only 0.015% of
its capacity.

More datasheets here:
http://data.energizer.com/datasheets/library/primary/lithium_coin/cr2025.pdf
http://data.energizer.com/datasheets/library/primary/lithium_coin/cr2016.pdf


- Franc Zabkar
--
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