我未用過呢部, 不過呢d好似係fast charge 舊電直到滿为止跟住就automatically change to slow charge, d BB声嘅作用係話你知差完啦。 所以fast charge 嘅時間唔会只得2分鐘咁少
may be your battery is half dead so the charger stops because it senses wrongly the battery is full. you can try to press the button again to fast charge when the charger change to slow charge mode. If the charger keeps change to slow charge mode quickly than your battery is properly dead.
just from my experience, already didn't use this type of charger for many years lu.