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ThinkPad T42 92P1011 Sony battery rebuild

T40/T41/T42/T43 Series
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kfzhu1229
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ThinkPad T42 92P1011 Sony battery rebuild

#1 Post by kfzhu1229 » Tue Jul 09, 2024 11:51 pm

For a while now I have the battery cells already spot welded into a generic 3S2P 6 cell pack and ready to go, but couldn't find a ThinkPad to attempt to rebuild on. But yesterday when I was going through my collection to check the status of all the battery packs, I found my T43 battery to be in dying condition (it's a T42 battery that last time I checked was still good). The voltage spikes and drops a lot, from 10.3V to 12V on charging.
I heard for T4x, people attempted cold swap rebuild with the BMS locking out. So, challenge accepted, I will demonstrate rebuild with my now very fluent hot rebuild process. The specimen today is a T42 battery from 2004 thank god, 92P1011, because it is SONY cells before the recall era!
Opening up the battery took some effort. Definitely harder than T/X6x but not like the HP Compaqs with the same shaped battery that are thoroughly epoxied together. I started prying from the inside away from the BMS board so cosmetic condition matters less. Took a while to gain an entry point, after which my flat head screwdriver did wonders. The sides had a pair of large clips that took a lot of persuasion to dislodge, but overall came apart with no major cosmetic damage, only small dents that I can mostly bend back with my fingernails. I did not open the rear side, I noticed the battery guts can slide out, so I slid it out and then with full access to insides, I gently dislodged the rear side clips to let it unclip with no prying and no damage.
One thing stuck out to me when I opened it up, I feel like it's malicious that they set a number of "traps" to mislead you! First, for whatever reason, if you have keen eyes on the gallery below, there are TWO long white positive wires, each going to the positive terminal on either side of the positive cells, and going to the BMS board but one goes to the current resistor (i.e. main rail) and the other one go straight to the BMS BQ chip??? Looks like a trap to me that if you sever their continuity, like what you would do with a cold swap, the fuse blows right away or something.
Furthermore, the white wires are positive, but the red wire is ground? What kind of misleading colour coding is this?
Anyway, first thing I did was to bridge the two positive pins on the BMS board so the trap can never activate.

Then, I took my spot welded pack, and did minor modifications, soldering on tabs where would be the most ideal locations for connection, match the connection points to as close to factory as possible. Then I also transferred across the original wax paper insulators.
And then I doubled up the wires, excluding the positive that is already doubled. Then I disconnected the original ground (red wire!), B1, B2, and the bottom B+ wire. I tape up the wire to not short against something on the BMS board
With a lot of fiddling, I was able to sit the new pack like so, connect the bottom B+ and B1 first, and then carefully pull the BMS board forward, on this side connect the ground and B2 wires
With this I can now completely disconnect the old pack out of the equation and connect up the other positive wire
With that wire for the 2 positive terminals still attached, I adjusted the soldering position of the plus wires to make sure they roughly match the length of original, and then removed that black jumper wire.
Then it's the process of taping up and gluing down so that the cables are managed as tidy as possible and make it as close to original and as safe as possible
Then after seeing the battery connector still has voltage, I applied liquid adhesive to glue the cells down on one half of the casing, letting it cure while making sure it's clamped down sitting as flush as possible
After it cured some, I tried powering on, it never lost power, so the laptop could turn on before I even attached the charger, and unsurprisingly it also charges perfectly fine
Lastly I make sure none of the broken plastic pieces remain inside the casing, and make sure plastics are straightened as much as possible, and then apply liquid adhesive to the edges and start clip the casing shut, with more clamping to make sure the casing sits as flush as possible. In hindsight maybe I should've glued and fitted these cells against the bottom half of the casing, since the rear edge of the cells protrudes over the casing slightly it was a nightmare getting those clips to align, and also the B2 wire initially got misaligned and caught, thank god I figured it out when the inside edge of the casing wasn't closing shut well, I aligned it properly before sealing it up for good...
Right now it is still in the process of clamping and waiting for the glue to dry, but so far the project is going more or less perfectly fine. I defeated IBM's traps on the BMS circuitry for this T42 Sony battery!
Full gallery: https://imgur.com/a/Tnzsz4b
Dell Lat CP MMX-233 64mb 40gb W2k
600 PII-266 416mb 40gb WXP
T23 PIII 1.13ghz 1gb W7
Precision M4300 X9000 8gb 160gb WUXGA Ultrasharp fp W10
T530i 15.6" i7 16gb fp W10
UXGA:
A30p PIII 1.2 1gb W7 (IDTech)
T43p 2.26 2gb fp W10 (Sharp)
Lat C840 P4-2.5 2gb 60gb W7 (Ultrasharp)

axur-delmeria
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Location: Metro Manila, Philippines

Re: ThinkPad T42 92P1011 Sony battery rebuild

#2 Post by axur-delmeria » Wed Jul 10, 2024 6:18 am

Excellent write-up! Makes me want to buy a spot welder to revive some battery packs myself.
Planned Purchase: T480s i5-8350 FHD Touch
Impulse Buy: Thinkpad not named for safety reasons :lol:
RIP: X220 4291-C91 X61 7676-A24 760XD-U9E :cry:

kfzhu1229
Senior ThinkPadder
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Posts: 2568
Joined: Tue Sep 22, 2015 10:59 pm
Location: Toronto, Canada

Re: ThinkPad T42 92P1011 Sony battery rebuild

#3 Post by kfzhu1229 » Wed Jul 10, 2024 4:20 pm

axur-delmeria wrote:
Wed Jul 10, 2024 6:18 am
Excellent write-up! Makes me want to buy a spot welder to revive some battery packs myself.
I'd say the difficulty of this rebuild was medium difficulty for my standards.
- Opening was not too easy not too difficult, once the wiring is figured out clearly it's not too difficult to replicate. Casing wasn't damaged in any major way, reassembly was also not too difficult
- The design of tucking all the cables through that gap inbetween 4 cells is kinda sketchy as fireworks can happen if you pinch them, fortunately I spot welded the majority of the battery pack so there was enough space for the cables to sit comfortably. I still had to check a few rounds to make sure no cables cross each other to minimise the possibility of pinching, and I even put kapton tape around the thick ground wire to make sure it cannot get punctured, and after what happened to my A31 battery I still lost some sleep last night thinking it could blow up when it was calibrating overnight even though I am very sure it is 100% safe now.
- All the original wax paper insulator were pretty mandatory. I pinched one of the cables when trying to close the case, if that wax paper is missing, it probably would've pinched against the body of the cell which could turn very ugly if it got punctured through.
- Hot swap was required (I believe), but seems like the first round of battery calibration goes smoothly, full charge capacity already went from 10Wh to 17Wh

And finally, I think this goes without saying if anyone replicates my work they're doing it at their own risks and of course don't hold me responsible if things go kaboom.
Dell Lat CP MMX-233 64mb 40gb W2k
600 PII-266 416mb 40gb WXP
T23 PIII 1.13ghz 1gb W7
Precision M4300 X9000 8gb 160gb WUXGA Ultrasharp fp W10
T530i 15.6" i7 16gb fp W10
UXGA:
A30p PIII 1.2 1gb W7 (IDTech)
T43p 2.26 2gb fp W10 (Sharp)
Lat C840 P4-2.5 2gb 60gb W7 (Ultrasharp)

kfzhu1229
Senior ThinkPadder
Senior ThinkPadder
Posts: 2568
Joined: Tue Sep 22, 2015 10:59 pm
Location: Toronto, Canada

Re: ThinkPad T42 92P1011 Sony battery rebuild

#4 Post by kfzhu1229 » Thu Jul 11, 2024 10:30 am

The battery gauge resetted quicker than I expected. I did 4 battery gauge resets with the old IBM power manager, the capacity went from 10 -> 17 -> 29 -> 45 -> 51Wh, and with my mix of LG 18650 MJ1's and LIshens against the ThinkPad BMS cutting power when there's 3.3V remaining per cell (these cells are designed to go all the way down to 2.75V at least), 51Wh turn out to be about the perceived capacity. Perfect match as I don't believe these BMS like to record any higher full charge capacity too far beyond designed capacity.
The battery casing also mostly sat perfectly flush except for 2 spots that needed some help from superglue.
Overall this was a great success!
Dell Lat CP MMX-233 64mb 40gb W2k
600 PII-266 416mb 40gb WXP
T23 PIII 1.13ghz 1gb W7
Precision M4300 X9000 8gb 160gb WUXGA Ultrasharp fp W10
T530i 15.6" i7 16gb fp W10
UXGA:
A30p PIII 1.2 1gb W7 (IDTech)
T43p 2.26 2gb fp W10 (Sharp)
Lat C840 P4-2.5 2gb 60gb W7 (Ultrasharp)

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