Why did the Ni-MH rechargeable battery I bought charge for a few days, and the lamp of the charger didn't change color?

First, check whether the positive and negative poles are well adjusted. If there is no problem, check whether there is a problem with the charger. If there is no problem, check whether the socket is powered on. Only when these three conditions are normal at the same time can the battery be charged! In addition: the charger's power indicator light no longer flashes, but always shows red, indicating that your battery is fully charged!