New laptop battery, bad runtime

fourthbean · February 22nd, 2006, 02:21 PM

I bought a laptop from ebay, as I expected the battery was shot. So I decided to rebuild it myself with new lithium cells. I bought the cells online with presolderded tabs and carefully rebuilt the pack. The battery now lasts for just over an hour instead of the 20 minutes of the former cells. But I believe the laptop should last for three hours on this pack. I have done all the calculations but would like for someone to look over them and tell me whether they are right.

The battery pack is made up of 4 cells totaling 14.8 volts, 2000mah a piece.
Inside linux when the battery is fully charged it shows battery capacity as 13000mW. When I unplug the power the current usage is anywhere from 9500mW to 14000mW.

The way I see it 13000mW is 13Whr's, am I correct? If that is the case then the capacity should be 14.8 X 2amp = 30Whr's. And that my laptop is pulling around 10 watts when running.

I suspect there is some circuitry that did not get reset when I put in the new cells. What I really want to know though is if my math is correct.

Thank you for any input you have,
Fourthbean

HeadBand · February 22nd, 2006, 02:40 PM

10W is pretty low...how did you figure this? and what are the specs of the system

fourthbean · February 22nd, 2006, 02:46 PM

Specs would have been a good thing to mention.

Compaq armada m300
p3 600mhz (not sure of wether it is the mobile one or not but I can turn the cpu down by 87%, so I think it is super mobile)
192mb ram
12GB hard drive
12.1" screen (difference between pulling 10W and 14W is the screen brightness mainly)

I got the ten watts from linux, with acpi enabled I can cat /proc/acpi/battery/C0F/state and it tells me that the current discharge rate is 10000mW/14000mW depending on my screen brightness.

I know that 10 watts seems low, especially when I think about the fact my amd processor in my desktop pulls 70 on its own.

When idling my cpu fan does not run and the laptop barely gets warm, so I know there isn't a whole lot of power being wasted.

Thanks for the quick response.

fourthbean · February 22nd, 2006, 10:53 PM

Bump for evening folks that would like to help me

fourthbean · February 23rd, 2006, 05:22 PM

Bump

mr.jiggyfly · February 23rd, 2006, 05:34 PM

Does it last an hour until ACPI tells you it is low, or does it last an hour before the voltage delivered by the battery gets so low that it shuts down?

Try running the battery down without ACPI getting in the way to see if the battery electronics needs to be reset.

fourthbean · February 23rd, 2006, 05:42 PM

I did check that as I read that it was a problem when you rebuilt a battery pack. I don't have any standby or suspend features on the laptop, and if I let it run it will die after an hour.