Battery gauge reset following cell replacement

[dandreye]

Hi All,

As a learning exercise I tried refurbishing one of my original IBM ThinkPad T42 4400mAh batteries with 6x dead Sony 18650 2200mAh cells inside using Sanyo 18650 2200mAh cells purchased off a top rated Ebay seller, reportedly taken out of a brand-new old unused battery. During the first 25-30min my refurbished battery loses 95% of the charge as its voltage drops from ~12.5V down to ~11.5V. When running Windows XP I can get another hour out of it afterwards if I disable shutdown upon reaching critically low charge threshold. Most of that extra hour its charge remains at 5% as the voltage stays within 11.0V-11.5V, only falling below 11V in the last couple of minutes (unfortunately I recall being unable to set that threshold any lower than 5% with Windows 7 when I tried that a long time ago). ThinkVantage Power Manager application v1.54 tells me that my refurbished battery only holds 17% of its design capacity (8.6Wh out of 47.5Wh). A couple of attempts to reset battery gauge using this application accompanied by complete charge-discharge cycles didn't make a difference. The seller says he tested all the cells by charging them up to 4.2V and making sure they hold their charge, which I'm inclined to trust. Is there perhaps something else I ought to do to tell the battery circuitry that it actually holds much more than it thinks it does, so that it stops misleading the laptop? Could the issue result from some well-known differences in Sony and Sanyo 18650 cell discharge patterns? All the soldering of the cells has already been checked and seems OK.

Many thanks in advance!

[RealBlackStuff]

You probably interrupted the battery's power circuit when you replaced the old cells.
Doing just one interrupt is enough to kill the battery charge circuit that's on a PCB in the battery.

[dandreye]

You probably interrupted the battery's power circuit when you replaced the old cells.
Doing just one interrupt is enough to kill the battery charge circuit that's on a PCB in the battery.

Thank you: I definitely did as I removed the old ones first (I did see the warnings not to but that looked too complex to do for me entirely on my own). However the discharge starts at ~12.5V as per Power Manager, which is about ~4.2V per cell that the seller has reported charging them up to, and charging stops only once that voltage is reached again... Do you mean those 12.5V reported by Power Manager can no longer be trusted?