wrong chargers kill batteries and may even set fire to your bike.
All my batteries with 21700 cells can be safely charged with 3A chargers. The 36V 20AH and 48V 15AH batteries can be charged with 4A chargers but you need to keep the charger where it is well ventilated because high current chargers produce a lot more heat. A 4A charger produces about twice as much heat compared to a 2A charger.
Like any fast evolutive products, battery longevity improves with product maturity. The problem with cheap batteries is you can't be sure that they don't contain relabelled cells, those which have been failed at QA check at the big manufacturers or fake branded cells. Even if you have only one bad cell in the pack, it can die early. As for new cases don't fit, it's easy to swap mounting rails or rack.
