until someone actually shows us the inside and we can figure out what failed, it is kinda impossible to make blanket statements about what failed or why. to imply that the failure is because of BMS battery built them poorly fails to acknowledge that these chargers are made by others and just sold by BMS battery. they don't know any more than you about them.
most of these chargers can be fixed easily, at very little expense. but we are a consumer culture, throw it away and buy a new one.
i have found that repairing this electronic stuff has forced me to learn electronics for the first time. in a really practical and useful manner. no wasted time studying laplace transforms and circuit equations. which i once did in a previous life.
just figuring out what the parts inside do has led me to be able to see them in the big picture format finally. kinda like richard and jeremy and wayne can see this stuff, but of course not at their level, but rewarding for me.