Thinkpads Forum

Hello,

I recently bought a X60s + ultrabase for fun and nostalgias purposes.
I already enjoyed installing a fresh windows xp sp3 + drivers and some oldies software and game.

Now I want to go ahead and try, for the challenge, to replace the battery cells. I already quite successfully open the battery and discover how everything has been connected.




And get the help of AI to generate this scheme:


I still have a lot of research to do and material to buy however (as you might already noticed), the battery isn't an original one. I search a bit but didn't find articles about replacing cells for clone batteries. If it's the same or different procedures.

If anyone has articles or advises it's more than welcome. I know that I can buy another battery for around 30$, however I'd like to learn this process for later recell batteries on a ThinkPad 600 (Pentium 2) and a Thinkpad x31 with a weak battery pack.

Thank you

Itstory

Welcome to the forum.

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Hi, I remember vaguely in the old days there was a warning or a rumour about a small IC inside the batteries that permanently needed some kind of power even if it was only a few volts. That if there was non-circuit situation then the chip would not be resurrected when power would come on. I never tested it out personally as I remember using jumper clips with similarly charged cell and swapped them in. Hope this helps, hope Im not perpetuating a ridiculous internet type meme

Hi, I remember vaguely in the old days there was a warning or a rumour about a small IC inside the batteries that permanently needed some kind of power even if it was only a few volts.

That's a quirk of most batteries after 2002-ish, they lock if the overall voltage drops too low or if the cells go too far out of balance. The BMS locking requires you to access the EEPROM chip that actually stores the BMS software, and reflash it to unlock it. Another user on the forums has actually made a lot of progress with this here, with original Lenovo OEM batteries.

Yours appears to be a cheap reproduction BMS, which is fine- but it's hard to say exactly what the BMS will do if it loses power. Maybe it will lock, maybe it won't. Depends on to what extent the makers of that knockoff BMS decided to implement. To be safe, it would be a good idea to maintain BMS power if you're attempting to recell it, most people will just solder any sort of power supply that maintains a voltage just below nominal (you'll have to look at the battery's label to get that) and leave that on while they detach the old cells from the BMS and attach the new ones.

Hey, that's some good info there. Never even thought it might be a BMS safety feature..

itstory wrote: ↑

Thu Jun 26, 2025 3:19 pm

I still have a lot of research to do and material to buy however (as you might already noticed), the battery isn't an original one. I search a bit but didn't find articles about replacing cells for clone batteries. If it's the same or different procedures.

If anyone has articles or advises it's more than welcome. I know that I can buy another battery for around 30$, however I'd like to learn this process for later recell batteries on a ThinkPad 600 (Pentium 2) and a Thinkpad x31 with a weak battery pack.

Thank you

Itstory

I've recalled countless X6x batteries by now, some original, some aftermarket. Some 4 cell, some 8 cell. I have my posts on a rebuild of 8 cell version of these on this forum.
Thing with this 4 cell aftermarket battery is that it is built in a very basic way. 4 cells, thin balancing wires running directly towards the terminals.
The upside is that this BMS is highly unlikely to give you troubles with it locking up after a full power disconnection. Swap on new cells and it will definitely work.
The downside is that the wiring is very primitive, and the safety standards are visibly much lower. In fact, this one seems to be very poorly built even for aftermarket battery standards. For example, if one of these wires get accidentally tucked under a cell instead of in between the cells, you'd see a firecracker. The BMS board is also most certainly lacking even basic safety devices, such as a real fuse, or even a real thermal probe! (these aftermarket BMS usually just have a placeholder resistor that makes the BMS always report 25C)
You can see my post and imgur album for a real 8 cell X61 battery for comparison.
The other problem is that these aftermarket BMS sometimes don't adjust the full charge capacity upwards correctly. This is always a gamble.
So I'd say, for practicing purposes, you can go ahead and invest in some bang for the buck battery cells. A 3000mah Molicel P30B for example would be quite good for this.
Take the battery rebuild slowly, one bit at a time. This is especially important for newcomers.
You might also need to invest in some insulation paper material as this aftermarket rebuild is lacking in terms of this. Some kapton tape also comes in handy. Any nickel strips coming off positive terminus MUST be insulated against the body of the cell!
It is recommended to spot weld the cells. I am not of the opinion to never solder cells or anything, but you'd need good skills and a decently competent soldering setup to do clean solder joints on 18650 cells. If you must solder, use a thick soldering tip, leaded solder and a tiny bit of flux, sand the cell terminals if they aren't new cells,. Tin a blob of leaded solder on the tip, and solder for 3-5 seconds max each time. Use 0.1mm thick nickel strips and it's highly discouraged to reuse existing strips - thicker strips require exponentially more powerful soldering iron or spot welders!
Let us know if there are any further questions.