Retro ThinkPad Battery Repairment

[Jifeng Chen]

I recently purchased a second-hand ThinkPad 240 with a dead battery, and I’m planning to replace the cells myself. I know that some relatively modern ThinkPads (e.g., X61, T61) have a Battery Management System (BMS) to manage the battery. In those cases, if you want to replace the cells, you usually need to rewrite the information on the BMS chip, or at least use a “hot replacement” method.

However, I’ve heard that for retro ThinkPads (e.g., the 200, 500, and 700 series), the battery management system is relatively simple. Can you just replace the cells directly and use the battery without any special procedure? Specifically, for a ThinkPad 240, would it be safe and straightforward to swap the cells myself, which seems much easier than dealing with modern ThinkPads?

[blegas78]

Just curious, I have a couple 760 series li-ion batteries and want to swap the cells in one but have been worried about the “suicide” BMS chips in that era.

I noticed that the Thinkpad battery utility can do a discharge/recharge cycle which I assume is intended for Ni-Mh batteries, though I am able to do this on my Li-ion packs. At first one of my batteries would charge only to 56% but then after running the battery cycle utility, the battery could be charged to 100%. I get these numbers are likely arbitrary, but I’m curious how the discharge utility fits into the BMS.

[Medessec]

However, I’ve heard that for retro ThinkPads (e.g., the 200, 500, and 700 series), the battery management system is relatively simple. Can you just replace the cells directly and use the battery without any special procedure? Specifically, for a ThinkPad 240, would it be safe and straightforward to swap the cells myself, which seems much easier than dealing with modern ThinkPads?

I've actually rebuilt Thinkpad 240 batteries already. And yep, their BMS chips don't need any sort of programming or procedure to reset them, just hook up the new cells and perhaps give the BMS a "jump" (momentarily bridge the 10.8V cell pack positive with the positive pin on the battery connector) and it should work right away. Of course, one or two full cycles will be needed to get the battery meter to be somewhat accurate again.

240 batteries in particular use 103450 prismatic cells, so you will need to find those as well if you want to do a proper rebuild. I imagine you could try to fit some other type of cell in there, like 14500s or Li-Po pouches, but I personally wouldn't recommend it if you want it to be reliable and close to original.

Just curious, I have a couple 760 series li-ion batteries and want to swap the cells in one but have been worried about the “suicide” BMS chips in that era.

I noticed that the Thinkpad battery utility can do a discharge/recharge cycle which I assume is intended for Ni-Mh batteries, though I am able to do this on my Li-ion packs. At first one of my batteries would charge only to 56% but then after running the battery cycle utility, the battery could be charged to 100%. I get these numbers are likely arbitrary, but I’m curious how the discharge utility fits into the BMS.

I've rebuilt multiple 760 Li-Ion packs with little trouble, although they are a bit time consuming to wire up because it's 12 cells. They are smaller cells, Panasonic CGR17500s which are not really able to be sourced nowadays, but the best substitute I've found is to use 14500 cells. Same length, just a bit thinner so I used thin foam to space them out a bit. One battery did end up completely dead after a few weeks of storage, it turns out one of the sets of 4 cells in series was 0 volts after I opened it up. I didn't see any charring or burning anywhere indicating something had shorted, so maybe that's the suicide BMS you're mentioning? But I think I have 3 more rebuilt batteries and they all have been problem free. And actually very useful because I have multiple 760s, and when diagnosing problems by switching parts around it saves me needing to have multiple chargers out and having wires going everywhere.

I've actually not been familiar with the discharge/recharge cycle in the battery utility, but I've just been running a game or other program (mainly JezzBall, lol) or just letting the 3D Maze screensaver play, with standby/sleep/turn off display, all those power saving features and timers turned off, and critical battery action turned off, so it runs all the way down to 0% and until the BMS cuts power due to undervoltage. It's generally how you get the BMS to reset it's battery level indicator (or gas gauge, it's called) and "calibrate" it. It's usually needed anyways after a cell swap. Even newer batteries are calibrated this way, although just to keep the meter accurate.

[blegas78]

That’s super helpful! Thank you! I just read another post that the “suicide” behavior is for the BMS chip itself, but it looks like that was more for batteries after 2002ish. Given your success with 770 batteries I may have to give it a go. I’m curious if you had to spot weld the cells, or does the thinness of those different cells provide enough breathing room for wiring?

Thanks for the reminder on Jezzball, haha. I recently picked up some old 760s on eBay due to feeling nostalgia so I’ve been frantically downloading all sorts of old games. I probably last heard/thought about Jezzball in the early 2000s, yet somehow I remembered exactly what it was reading your post

[Jifeng Chen]

Just curious, I have a couple 760 series li-ion batteries and want to swap the cells in one but have been worried about the “suicide” BMS chips in that era.

I noticed that the Thinkpad battery utility can do a discharge/recharge cycle which I assume is intended for Ni-Mh batteries, though I am able to do this on my Li-ion packs. At first one of my batteries would charge only to 56% but then after running the battery cycle utility, the battery could be charged to 100%. I get these numbers are likely arbitrary, but I’m curious how the discharge utility fits into the BMS.

Also curious for me, I guess maybe after I get my Thinkpad and rebuild the battery, I may have an answer for you. But guessing from the phenomenon, it's just a lack of recalibration? Like after running the discharge/recharge cycle, it has actually done a recalibration and so you can charge to 100%?

[Jifeng Chen]

However, I’ve heard that for retro ThinkPads (e.g., the 200, 500, and 700 series), the battery management system is relatively simple. Can you just replace the cells directly and use the battery without any special procedure? Specifically, for a ThinkPad 240, would it be safe and straightforward to swap the cells myself, which seems much easier than dealing with modern ThinkPads?

I've actually rebuilt Thinkpad 240 batteries already. And yep, their BMS chips don't need any sort of programming or procedure to reset them, just hook up the new cells and perhaps give the BMS a "jump" (momentarily bridge the 10.8V cell pack positive with the positive pin on the battery connector) and it should work right away. Of course, one or two full cycles will be needed to get the battery meter to be somewhat accurate again.

240 batteries in particular use 103450 prismatic cells, so you will need to find those as well if you want to do a proper rebuild. I imagine you could try to fit some other type of cell in there, like 14500s or Li-Po pouches, but I personally wouldn't recommend it if you want it to be reliable and close to original.

Thank you so much, luckily I have some 103450 from Panasonic. Even more luckily, my 240 is attached with a large battery pack with 18650 cells. But may I ask, how did you solder the cells — did you use a regular soldering iron? I’ve seen many people say that a spot welder should be used instead.

[Medessec]

That’s super helpful! Thank you! I just read another post that the “suicide” behavior is for the BMS chip itself, but it looks like that was more for batteries after 2002ish. Given your success with 770 batteries I may have to give it a go.

Ah... so you mean when the BMS decides to softlock and prevent any discharge of the cells if it detects some sort of failure? Me and another old laptop enthusiast are trying to work on that for the 2001-2005 batteries, and 2005-onwards batteries can be reset with the right tools if you know what you're doing... but it is not much less tricky.

Yeah thankfully all the really early Li-Ion stuff is just a cell swap, but that doesn't mean it suddenly becomes "easy". Anyone attempting such a rebuild should take it seriously and definitely factor in safety. Don't try to mix and match salvage cells and tape them together like I did for a time. You're just asking for trouble.

Thanks for the reminder on Jezzball, haha. I recently picked up some old 760s on eBay due to feeling nostalgia so I’ve been frantically downloading all sorts of old games. I probably last heard/thought about Jezzball in the early 2000s, yet somehow I remembered exactly what it was reading your post

Heck yeah dude! Jezzball, Pipe Dream, Chips Challenge, I forgot what that one weird one was called where the mouse is in the center and the cats are on the outside randomly moving about... but dang, that was my childhood for sure. Oregon Trail Deluxe and Roller Coaster Tycoon as well. I always love going back to it, glad I woke those brain cells back up for ya again!

Just curious, I have a couple 760 series li-ion batteries and want to swap the cells in one but have been worried about the “suicide” BMS chips in that era.

I noticed that the Thinkpad battery utility can do a discharge/recharge cycle which I assume is intended for Ni-Mh batteries, though I am able to do this on my Li-ion packs. At first one of my batteries would charge only to 56% but then after running the battery cycle utility, the battery could be charged to 100%. I get these numbers are likely arbitrary, but I’m curious how the discharge utility fits into the BMS.

Also curious for me, I guess maybe after I get my Thinkpad and rebuild the battery, I may have an answer for you. But guessing from the phenomenon, it's just a lack of recalibration? Like after running the discharge/recharge cycle, it has actually done a recalibration and so you can charge to 100%?

Hard to say without actually seeing what your cell voltages are, it's very possible that one part of the whole pack is degraded to the point where it's actually hogging voltage from the rest of the pack. The old ones really just tracked battery life with a series of timers and voltage/current sensors, and it doesn't really do anything super complex other than balance the cells by applying small currents to the cells in different series voltages. If you wired all new cells up with good connections, it would be fairly accurate after one full discharge and charging cycle.

Thank you so much, luckily I have some 103450 from Panasonic. Even more luckily, my 240 is attached with a large battery pack with 18650 cells. But may I ask, how did you solder the cells — did you use a regular soldering iron? I’ve seen many people say that a spot welder should be used instead.

I do have a spot welder, and as far as welding to the cells themselves- yes, that's the way to go. Unless you have a very powerful spot welder, using the original nickel strips is very difficult... plus they tend to get all mangled when you pull them off the old cells, so it's a good idea to get a roll of new nickel strip. Make sure it's enough for the current you expect to go through it, and depending on the spot welder you have- you may also want to sand the surfaces a bit of both the cells and the strip where you plan to weld it. I have a Fnirsi SWM-10 which works okay for small to medium level jobs and has been a solid spot welder. Using a soldering iron isn't advisable on prismatic cells... the heat you have to apply to get the solder to stick can harm them or bust the fuse.

I’m curious if you had to spot weld the cells, or does the thinness of those different cells provide enough breathing room for wiring?

The wiring that goes back to the BMS fits very easily yea because of the thinner cells, but yeah I do remember- on the EBL 14500s I got, I had to grind the button off to get them to fit properly, which made them tough to spot weld to.

[Jifeng Chen]

I do have a spot welder, and as far as welding to the cells themselves- yes, that's the way to go. Unless you have a very powerful spot welder, using the original nickel strips is very difficult... plus they tend to get all mangled when you pull them off the old cells, so it's a good idea to get a roll of new nickel strip. Make sure it's enough for the current you expect to go through it, and depending on the spot welder you have- you may also want to sand the surfaces a bit of both the cells and the strip where you plan to weld it. I have a Fnirsi SWM-10 which works okay for small to medium level jobs and has been a solid spot welder. Using a soldering iron isn't advisable on prismatic cells... the heat you have to apply to get the solder to stick can harm them or bust the fuse.

Thank you so much! I was actually wondering if I could do it myself using just a soldering iron, but I found that many spot welders are quite expensive. I really appreciate your advice — it’s very helpful. Also, thanks for recommending the welder. I just looked it up, and it really does seem like a great and affordable option.