T720 battery question

I think I dropped the phone one time too many. It's dead. Putting it on
charge made the screen backlight come on and sometimes it would say
"Charging" but nothing else. Would not turn on.

I took out the battery and probed the 4 contacts in every combination with
a DMM and got no readings. Figuring I have nothing to lose I peeled off
the sticker and pried it open. I do read voltage on the power cel. So I
figure that bit of micro circuitry has been damaged. Anyone know what it
does? I figure some of it is some sort of current limiter and maybe
something is a micro fuse of some sort and that might be the failure point.
Is there anything that can be bypassed?

I've already ordered a replacement battery (even though I really should
just get a new phone) but it would be nice if I could make this battery
work again. Also just general curiousity about what that circuitry is.

Steve Kraus wrote:
>
> I took out the battery ...
> I ... read voltage on the power cel. So I
> figure that bit of micro circuitry has been damaged. Anyone know what it
> does? Is there anything that can be bypassed?
>

It's a protective circuit. It has a fuse to protect against heavy
currents such as short circuit and a circuit to limit charge. When a
lithium cell is charged beyond 4.1-volts metallic lithium is created.
This can result in a vigorous chemical reaction where the battery gets
very hot, bursts, and the material inside catches on fire when exposed
to air.

If this appeals to you ... bypass the protective circuit.

Regards, Gordon>

> It's a protective circuit. It has a fuse to protect against heavy
> currents such as short circuit and a circuit to limit charge. When a
> lithium cell is charged beyond 4.1-volts metallic lithium is created.
> This can result in a vigorous chemical reaction where the battery gets
> very hot, bursts, and the material inside catches on fire when exposed
> to air.
>
> If this appeals to you ... bypass the protective circuit.

Heheh...I would've taken my chance with the fuse for a day til the new one
arrives (hopefully tomorrow) if in fact that's what it was and failed from
mechanical shock, but obviously not current regulation. Quite a few tiny
parts on a very small board. Needs further study.

This is the phone that survived being driven over largely unscathed. Lost
the outer LCD function, and just a few pixels off the main color screen; I
successfuly replaced the entire 2 screen plus vibrator module. That was
2.5 years ago. I'm overdue for a new phone but I dread the whole
shopping/choosing thing and fear ending up with one I hate. I think this
must be phone number 4 and it's the first one I've liked. But I digress...