Li-Ion stored flat for 2 months

[John Savage]

I found a Nokia 7250i on the street and kept it switched on for 3 days
expecting the owner would ring its number. No one rang and by that time
the battery was flat so I handed the phone to the police and it has now
been returned to me 10 weeks later, so its battery has been flat all
that time.

A friend tried to recharge it with his Nokia charger but says after 30 mins
or so it still was not charging, just appeared dead. Is the battery junk or
is it the cell's electronics that is preventing it from accepting charge?
Is there a way to resuscitate it? I seem to recall reading on some newsgroup
there's a technique to momentarily bypass the electronics to get things
moving.
--
John Savage (my news address is not valid for email)

[Mark H]

> A friend tried to recharge it with his Nokia charger but says after 30
mins
> or so it still was not charging, just appeared dead. Is the battery junk
or
> is it the cell's electronics that is preventing it from accepting charge?
> Is there a way to resuscitate it? I seem to recall reading on some
newsgroup
> there's a technique to momentarily bypass the electronics to get things
> moving.

Try a 5.7v charger overnight. Often, a new or completely flat battery will
not show as charging or holding charge for an hour or two after you plug it
in, something to do with trickle charging to make sure it wont explode IIRC.

-mark

[budgie]

On Fri, 13 May 2005 01:31:12 GMT, John Savage <rookswood@suburbian.com.au>
wrote:

>I found a Nokia 7250i on the street and kept it switched on for 3 days
>expecting the owner would ring its number. No one rang and by that time
>the battery was flat so I handed the phone to the police and it has now
>been returned to me 10 weeks later, so its battery has been flat all
>that time.
>
>A friend tried to recharge it with his Nokia charger but says after 30 mins
>or so it still was not charging, just appeared dead. Is the battery junk or
>is it the cell's electronics that is preventing it from accepting charge?
>Is there a way to resuscitate it? I seem to recall reading on some newsgroup
>there's a technique to momentarily bypass the electronics to get things
>moving.

Electronics (usually in the battery package but in cellphones it is cheaper
built into the phone itself) generate the actual shutdown, typically when the
cell reaches 3v0. Although self-discharge in Li-Ion is low, it isn't negligible
so the voltage will have dropped further. This puts the battery in a "lockout"
state where a high impedance is present in series with the cell.

The normal way to recover from this state is patience with the charger. As only
a tiny charge can be administered in this state, it takes a long time to
increase the cell voltage above the lockout threshold - usually several hours.

Just leave it on the (correct) charger. If it doesn't come good within a day or
two, it's f#sked.

[John Savage]

"Mark H" <nukeleerATinternodeDOTonDOTnetREMOVECAPSAU> writes:
>Try a 5.7v charger overnight. Often, a new or completely flat battery will
>not show as charging or holding charge for an hour or two after you plug it
>in, something to do with trickle charging to make sure it wont explode IIRC.

I have a lab power supply so I'll try charging it from that. Would you
know whether the centre pin of the charger plug is +ve or -ve ?
--
John Savage (my news address is not valid for email)

[Mark H]

> I have a lab power supply so I'll try charging it from that. Would you
> know whether the centre pin of the charger plug is +ve or -ve ?

You haven't left it charging in the phone yet?

Oh well. Use a multimeter or LED to double check, pretty sure the centre
charger pin is +ve

-mark