K7300 NiMh/NiCd battery charger/discharger

hello lads. i would like some help
can someone please tell me what exactly does the LM324 do?
It compares the present voltage of the battery to the desirable selected voltage via the jumper and then it decides wether the battery needs to be discharged or not ? or am i wrong?
and also a second question
at the k7300 manual booklet at page 14 at the 28.diagram check out the A4 (1/4 operational amplifier) under the LED1 DISCHARGE …that just stands there all alone…shouldnt be connected to something ? is there a mistake at the drawing?
thank you
looking forward for your replies

You are correct regarding the operation of the op-amp.
The circuit only uses 3 op-amps. LM324 is a quad op-amp, so one is not used.