Battery cells brand, depreciation, and production date is a big deal. There is a calendar life on Li-Ion batteries; you don’t want to surprise yourself with a dead battery which costs 50% of the value after a year or so.
Li-Ion battery packs can be quite cheaper and more dangerous if not being manufactured under certain standards, qualifications or inspection. There have been many catastrophic battery explosions in Canada and the US in the past year due to poor quality battery packs that have been supplied under famous brands like Panasonic. You might like to pay more for digital and display features, brand names, high end bicycle components especially for suspension mountain bikes; however the weight, durability, performance and the quality of motor/controller/battery will not vary much.