T4x Battery repair / cell replacement

[jt20]

Do the circuit boards in these batteries fail often? In think I may have good cells but a bad chip.



Apparently I know nothing about Thinkpads - I couldn't even order the right battery.
The Lenovo outlet was offering S/D 9-cell replacements but it was: ThinkPad T/R/W/Z/SL Series 9 Cell Li-Ion Battery and does not work on the T42.


So I took out the cells and re-wired them onto the casing that fits, along with the old chip. The rating for this battery is slightly higher (7800 Ah) but the voltage is the same. I thought this might be due to the chip. The casings and battery configuration are the same except for the plug into the computer.

my comp will not run for long on the battery nor does it seem to be registering charge with the new cells.

*do the chips in these batteries go bad along with the cells?*

Or am I fighting a lost battle?

[SteveS]

I would give up on this battery.

I don’t know the specifics of the Smart Battery chips used in Lenovo battery packs, but I can relate what I have read on the specification sheets for this type of IC. These chips usually do not have non-volatile flash memory cells in them. (This is because the IC process needed for the power and power sensing circuits used in these chips can not support flash memory architecture). Therefore the memory used is static CMOS ram, which requires some level of power to maintain it. Because the chip is hard connected to Li-Ion battery cells, it is always assured of having power applied. (The chips do not allow the external load to ever fully discharge the battery to 0 V). So all the battery specific information stored in chip such as serial number, maximum capacity, date codes, etc, are written into a finished battery at the factory using a fixture and a special software routine. If you ever disconnect the chip from the battery cells, this information is lost when the power is removed. Once this happens, the chip no longer has information it needs to be able to regulate charging. For safety, most chips will not allow the battery to be charged if the data is either missing or corrupted.

I have read articles in other forums giving instructions on how to swap cells in other brand laptop batteries. These always require a step to jumper the cell connection to an external source during the replacement, to keep the chip powered.

In general, opening a Li-Ion battery pack can be dangerous and something I would never recommend. The batteries are constructed to make it difficult to open. Accidently shorting a cell before the fuse protection can result in a fire or explosion. Pouring water on a burning lithium cell will result in an explosion, as the reaction will release hydrogen and a lot more heat.