X41 Tablet Battery Issues

[rototype]

Hi All,

Got an unusual problem with my X41 Tablet. When I got it, it booted from battery OK, and went into BIOS (there was no HDD at the time).

Finally got a HDD etc.. and loaded up XP Tablet (plugged into mains). Somewhere along the line I must have let it run the battery flat as it won't talk to the battery any more. The battery monitor in XP says 'No Activity' and reports 75% capacity remaining, althoughif I pull the power lead out it dies instantly.

I've got the battery apart and tested each of the cells and they're all reading around 3.85V (one's nearer 4V but I suspect a bit of variance is usual). I now suspect that there is something electronic at fault on the board. I've identified a couple of chips :- there appears to be an EEPROM chip on the rear of the board (S24C01BDE8), A set of 4 TPC8111 chips around the output area, a bq80201DBT battery level chip and 2 bq29312PW chips (3-4 cell battery protection).

Anyone got any idea where to look on this board, or what needs to be changed, or even anyone got a circuit diagram or schematic for the battery? Failing this does anyone know where I can get a replacement board fairly cheaply.

Many Thanks

[topmahof]

All batteries have a smart chip in there that monitors the battery. If it detects a problem with the cells, voltage differences, overheating of the cells, shorting, it sends out a flag. Depending on what power manager the computer is using, the battery could keep working or be shut down.

A genuine Lenovo battery has a safety in there which actually shuts it down when the smart chip detects a problem.

Most batteries will rewrite the eeprom on a command from the computer which resets the smart chip. On a Lenovo battery this feature is disabled. So you have a dead battery.

Sellers on ebay advertise that they will take any and all dead batteries and what they do is recell the batteries with cheap cells and rewrite the eeprom and sell the battery as a new battery.

Rewriting the eeprom resets the charge cycles back to 0, gives it a new manufacturing date and gets rid of the flag that shut the battery down in the first place. If you run the serial number on the battery you would find that there are 2 manufacturing dates, the original from the serial number and the second that power manager sees. That's how you can tell whether you have a new battery or one that has been recelled and reset.

An eeprom writer is not cheap, but there are free programs everywhere that can be used to reset the battery eeprom.

Rewriting the eeprom on your battery will make it work again, but the cell problem that shut it down in the first place will still be there and Lenovo's smart chip will just shut it down again unless you recell the battery. There's white paste on some of the components on your board, if any of that paste is discolored then that board is probably fried.

All of this came out after the big battery recalls in 2005 and since. Sony developed a new crimping procedure for manufacturing their cells which introduced impurities into their cells which caused some batteries to overheat, short, and actually explode and catch fire.

[rototype]

Many thanks for that, eeprom writing shouldn't be a problen (I have the technology!...) There's no discolouration on the white stuff (non technical term but accurate enough) could one of the tpc8111 chips be at fault? I have a fairly good idea that the cells should be OK, Is there anything else that could be at fault?

Tim

[topmahof]

You don't show any output on the battery connectors themselves, right?

Most battery smart chips are connected directly to the cells, but in the case of a Lenovo battery there's another chip in there that actually shuts it down if the smart chip detects a problem. And it could have been a one time problem. Overheating, a cell voltage fluctuation. I've never traced out one of those battery boards, I always just reset the eeprom and hoped it worked. 1 out of 3 doesn't work. Usually when you get rid of the flag that shut it down in the first place, it'll work. If you have a good eeprom reader and writer, you should be able to read the code that shut it down. My board's pretty basic, can't read codes, it just resets everything to its defaults.

And yes, one of those tpc chips could be the problem, although if one of those was bad, you still should get at least some kind of reading on the battery connectors.

http://www.summet.com/blog/2007/02/17/l ... ry-refill/

This might give you a little more information. There's a fuse in there along with a thermocouple.