Have seen these panasonic cell packs advertised https://www.amazon.de/Akkupack-Panasonic-NCR18650PF-Lithium-Ion-Entladestrom/dp/B01KNXAPLC . They look good quality and pre-welded but i would need to fit a BMS, which is just soldering work.
I can re-use the BMS off the old battery but might want...