Can someone explain the workings of this charger schematic?

I took apart my Black and Decker cordless drill charger, and drew this schematic to my best ability. I am trying to understand it to my best of my ability and what each component is responsible and how it charges the battery.

From my understanding D1 only allows energy to flow to the battery. But if the potential of the battery is lower then the charger's shouldnt that be not a problem? Since it will always be more and push the electrons to the battery?

The resistor and the LED are understandable, but the job of NPN (might be wrong ) transistor is a mystery to me.

Picture of Can someone explain the workings of this charger schematic?
iceng5 years ago
No real explain...... Lots of things wrong here.
Sorry the NPN does nothing for charging.
The 5k in series with the LED allows only 3ma to light it ?!
The base of the transistor is driven by the D2 diode drop ?

Eax5 (author)  iceng5 years ago
I wasn't sure if it was the right part. The numbers that were on the back of the component are 2N5551148. I didnt find anything with those numbers so I looked up 2N5551 and it said it was NPN