The situation you described should be caused by the lack of water inside the battery! [Why is there a lack of water; because in charging the battery is a process of converting electrical energy into chemical energy! Heat and gas will be generated! There are some skin caps on the battery cover that are used to vent the water out of the battery.]
The solution; [note] if the warranty has expired you can do as I said; open the cover, remove the skin caps and inject 2 tubes of battery replenishment fluid with a small hospital syringe [available in the market] into each hole, then charge it, and it will definitely jump the green light! Then turn the battery upside down for 10 minutes to drain the excess fluid and seal the cap! Then use up the power [loaded and used up] and charge again; if the time is more than 3 hours the battery should be fine Of course the warranty period is not up you still go directly to the dealer.
On the issue of battery maintenance First of all, pay attention to the throttle not all the way to the top when you start the best with your feet on the ground pedal down [booster] 2 general normal riding as long as you add to the throttle 3/4 position 3 do not overload [overloaded] 3 the best to travel at a constant speed 4 when the power meter suggests that the electricity to be used up do not force the driving replenishment of electricity and then ride again. 5 must be full of electricity and then use the e-bike. [To charge it should be full or not]
I hope it can help you ，，，，，