# Laptop power question 2: dead battery

K

#### Keiron

Hi again,

If a laptop battery is dead, like mine which holds about 45 seconds of
power, are there power advantages to running the laptop without the
battery installed? For example: Will it draw less power; be more stable?
I suppose indirectly I'm asking how does a laptop treat a diminished
capacity battery: will it treat it as simply a lower capacity and once
it's been filled with charge just leave it or will in constantly be
trying to charge it to somewhere near it's original capacity?

Thanks

P

#### Paul

Keiron said:
Hi again,

If a laptop battery is dead, like mine which holds about 45 seconds of
power, are there power advantages to running the laptop without the
battery installed? For example: Will it draw less power; be more stable?
I suppose indirectly I'm asking how does a laptop treat a diminished
capacity battery: will it treat it as simply a lower capacity and once
it's been filled with charge just leave it or will in constantly be
trying to charge it to somewhere near it's original capacity?

Thanks

Some charging circuits are intelligent enough, to not attempt
to charge a flat battery.

http://www.batteryuniversity.com/partone-12.htm

"The safety circuit is designed to cut off the current path if the
battery is inadvertently discharged below 2.50V/cell. At this voltage,
most circuits render the battery unserviceable and a recharge on a
regular charger is not possible."

I have no idea what a laptop uses for charging, but it does have to be
careful with that kind of battery.

Paul

B

#### Brian Cryer

Paul said:
Some charging circuits are intelligent enough, to not attempt
to charge a flat battery.

http://www.batteryuniversity.com/partone-12.htm

"The safety circuit is designed to cut off the current path if the
battery is inadvertently discharged below 2.50V/cell. At this voltage,
most circuits render the battery unserviceable and a recharge on a
regular charger is not possible."

I have no idea what a laptop uses for charging, but it does have to be
careful with that kind of battery.

Presumably if in doubt then its better to take the battery out?

M

#### mm

Some charging circuits are intelligent enough, to not attempt
to charge a flat battery.

http://www.batteryuniversity.com/partone-12.htm

"The safety circuit is designed to cut off the current path if the
battery is inadvertently discharged below 2.50V/cell. At this voltage,
most circuits render the battery unserviceable and a recharge on a
regular charger is not possible."

This has to be for a battery charger that is doing nothing but
charging a battery.
I have no idea what a laptop uses for charging, but it does have to be
careful with that kind of battery.

Paul

But a laptop power supply isn't just charging the battery, it's
powering the computer, and for sure it's doing so when the output
voltage of the battery would be very low. So it can't turn off or
the computer would not work.

Some circuit might interrupt battery charging, but the circuit would
have to be in the laptop, and I don't think it would be practical,
since most people have no other way to charge their laptop battery
except in the laptop, and if the the charger wouldnt' work at very low
battery voltage, what would the user do. And at least there should be
computer for 30 seconds iirc, but it still needed to be recharged, or
it wouldn't do that. 30 seconds was enough to unplug the cord and
move to another nearby electrical outlet, so I valued those 30 seconds
(later 15 iirc.)

I'll go back to asking questions and lurking now.

P

#### Paul

mm said:
This has to be for a battery charger that is doing nothing but
charging a battery.

But a laptop power supply isn't just charging the battery, it's
powering the computer, and for sure it's doing so when the output
voltage of the battery would be very low. So it can't turn off or
the computer would not work.

Some circuit might interrupt battery charging, but the circuit would
have to be in the laptop, and I don't think it would be practical,
since most people have no other way to charge their laptop battery
except in the laptop, and if the the charger wouldnt' work at very low
battery voltage, what would the user do. And at least there should be
computer for 30 seconds iirc, but it still needed to be recharged, or
it wouldn't do that. 30 seconds was enough to unplug the cord and
move to another nearby electrical outlet, so I valued those 30 seconds
(later 15 iirc.)

I'll go back to asking questions and lurking now.

I don't know anything about the charging policy. I have a grand total
so far, of one laptop schematic here, and it's a joke of a schematic.
So I'm no further ahead on getting info on the topic.

The charging circuit has to follow safe practice, whatever that is.
On some battery types, you could dump charging current into them
(in vain), for as long as you want. A NiCD with a dead short inside,
probably doesn't care that you're trying to charge it. Lithium
chemistry could be different, and that's why I selected the
batteryuniversity article as an example. The laptop does have sophisticated
power management in it, and it isn't a dumb charger like the one on my
cordless screwdriver. The dumb chargers definitely damage batteries,
but the battery type is such there are no safety issues, only cost
of replacement as an issue.

Paul