We do offer a repair service, based in the Netherlands for the Nao Robot battery pack. The type we already repaired is model 6S1P, US18650NC1, 6INR19/66 from Softbank Robotics Corp. Capacity 62.5Wh, 21.6V / 2.9Ah.
Only quality cells from Sony, Panasonic or Samsung are used. It depends which are locally available at that time. Capacities vary around Typ. 2900 mAh, discharge current will be rated Min. 10A. All six batteries inside the pack will be replaced with new (non-refurbished) cells.
Please contact me (Marco): NaoRepair at Makerspace040 dot nl or Whatsapp, Telegram or Signal me at +31 (six) 2035 (zero) 823.
The individual cells will be properly spot welded and kaptop tape will be used identical to the original battery construction. To open the pack we will have to saw through the clips holding the pack. We will glue the pack together with a 2 component epoxy glue.
Due to the way we need to open up the glues pack, the structural strength of the battery pack will be less strong as the original. Do not charge or use the battery pack unattended.
We started this service because there is no support from the manufacturer, and also the batteries are incredible expensive. From the site https://www.bartneck.de/2021/02/03/repair-of-broken-nao-robot-battery-pack/ we also concluded that people could well be interested in this service. Repairing is almost always better than throwing it away.