Broken Charger-connection Alert

[walid]

The circuit shown below is from: http://www.redcircuits.com/Page86.htm



For me, it is easy to analys any circuit containing npn transistors, but i'm confused when come face to face with pnp type

i read this in the same page:

Circuit operation:

The circuit is inserted between the supply and the load, therefore, until a trickle-charging current of at least 100µA is flowing towards the load, D1 and D2 will conduct. The forward voltage drop (about 1V) available across the Diodes, drives Q2 into conduction and, consequently, Q1 will be cut-off.
If no appreciable load is connected across the circuit's output, Q2 will become cut-off, Q1 will conduct and the Piezo-sounder will beep.

Assume that I insert this circuit between a 13.7v charger and a small 12v battery, can anyone explain what will happen at first and when the batt is fully charged.

thanks