does this charger use a timer to tell if the batts are charged or it can tell by the current in them?

coz i charge half way then nd to use the socket, say i charged initialy for 3hrs.

then i continue charge for another 6hrs?!?!before then light turned green?

will i be over charging them.

they are gp 2100mAh.

and one more thing can i use it to charge recykos?

thks! cheers