Inside a cloned Thinkpad 61++ 01AV427 Battery (For T480/T580)

With the purchase of my new Thinkpad T580, I was excited to see that the internal battery was at an amazing 90% health after several hundred cycles. The external battery however, did not fare so well. It came with the slim model 61 battery (24Wh) and it was reporting only 5% of its design capacity left. I had to buy a replacement.

Seeking reprieve from everyone’s favorite massive conglomerate, Amazon, I found a model 61++ replacement pack for $35. The battery was absolutely a clone, no proper Lenovo branding visible. Unfortunately nowadays, clones are your only real option for the T480/T580. Any new old stock 61 series batteries may not have retained their original capacity. In addition, any official units you can find through any reputable channels are prohibitively expensive on top of that. To top it all off, despite being advertised as a 72Wh battery and having its rated capacity report as such, after several cycles HWINFO still reports the actual capacity as approximately 58Wh… Disappointing.

Having 2 years of lithium battery pack assembly experience, I was of course curious and had to open it up. Seeing as there were hints at the larger capacity batteries utilising 18650 cells, I could only wonder if better cells could be used.

Opening chinese clone batteries is usually much easier than OEM units and this was no exception. Some careful prying at any visible seams yeilded an easy win for opening without major damage (although some tiny clip pieces were liberated into low earth orbit, the top still would eventually close again).

Inside is pretty standard for any laptop battery pack based on cylindrical cells. Six 18650 cells spot welded into a 3s2p format to achieve the required 11.1v nominal voltage.

Looking closer at the cells, they are semi-generic chinese cells that at least have a model printed on them, JDDL INR18650E, and a (stated) capacity of 2500mAh each (Not the Sony cells reported by HWINFO! Who could have seen that coming?). Some light Googling didn’t yeild any datasheets or specs for the “E” variant, but they did show at least a “P” variant with a stated max discharge rate of 7.5A.

I neglected to photograph the spot welds and nickel, but I suspect they are using nickel plated steel. The spot welds themselves look relatively weak and could probably be pulled off leaving a clean surface on the cell. Not a good bond with the cell casing. Another thing I was not a huge fan of was the lack of using extra insulation rings on the cell positive ends. Leaving these off poses more of a risk for shorting to the cell wall if the fragile wrapping is damaged.

I very quickly noticed this on the BMS, “LEN X260-R1”. Is this an OEM Lenovo BMS ripped from a Thinkpad X260 battery? Or was this a cloned BMS that was developed for use with many other batteries? Possibly originally the X260? Due to the firmware version being all zeroes in Lenovo Vantage, I would say the latter is most likely unless the firmware only was hacked.

Likely being the latter, that is actually a good thing. Many of the chinese clone BMSes are less restrictive than OEM Lenovo BMSes in that they won’t brick themseleves when the cells reach 0v. All thats required to remove them is disconnecting the balance leads in a specific order and jumping the output when finished to “enable” it again. This also opens up the possibilty of getting the cheapest version of these batteries and ripping out the over-rated cells and replacing them with something much better, like the Molicel M35A.

With M35A cells in the 3s2p configuration, the resulting pack would actually have a capacity of 77.7Wh which is even more than Lenovo offered back then. These chinese cells, labeled 2500mAh, would on a good day only be producing 55.5Wh of capacity. Thats only 77% of the advertised capacity! M35A cells range in price from $5 to $7 each, so finding a cheap clone battery and swapping out the cells for something more reliable and higher capacity seems like the best way to go for making the most of your external battery experience. For now I plan to ride these cells into the ground or until I get fed up with them, then I will attempt a swap.

I pimarily dealt with 21700 sized cells at my previous job and they are my favorite form factor to energy density format. That got me thinking, what if… a custom 3s2p 21700 pack with the highest capacity cells in the form factor, 5000mAh?

Granted these are 4200mAh Molicel P42A cells in the picture, but something as simple as the Samsung 50E would suffice. With a whopping total capacity of 111Wh, that pack alone rivals many people’s configuration with both internal and external packs.

Doing this would definitely require a custom modeled case though, but it could for sure be done. The cells would have to be placed completely below the chassis since the longer 70mm length wont quite fit in the original cutout of the laptop. Elevated at an angle as shown would be ideal to retain the original length of the bulge of the pack.