Over discharge cutoff for 6v lead acid batteries- hysteresis

Hi all
i have recently built this circuit to cuttoff two 6V batteries when thy reach approx 4,5V.
The problem im having is establishing hysteresis with positive feedback.
The relay chatters when reaching the cuttoff zone.
Im using a rail to rail opamp.
I have tried numerous resistor values between opamp output pin 1 and the + non inverting input, all with no luck.
Can anyone help me please.

Welcome to ETO!
The non-inverting input is being clamped by the zener diode.
Add a resistor (say ~10k) between the non-inverting input and the zener cathode, then try the feedback resistor to that input.

I agree with alec_t. Also, you need a lot of hysteresis, as the battery voltage will jump up as soon as the load is removed.