this is a schematic for a 12v rechargable battery circuit it has overcharge protection.
im wondering what component values i need to change in the circuitry to make it able to charge a 24v sealed lead acid battery (2x 12v batteries in series).
If this ciruit is not good enough to charge a 24V battery, which other circuit could I use that would work?

 

Your schematic is incomplete, as there is no source of power shown.

How about just telling what you want to accomplish, for example 1A (10A?) charger for 24V SLA, powered by x (120v AC?), with features y & z (overcharge protection, 3-zone charge strategy, etc.)

 

our battery is a 7ah 12v sealed lead acid battery connected in series to give 24V.
What value should the transformer step down the voltage to? From 230V AC down to say 32V DC.
The circuit above is a charger controller that stops and starts charging for a 12V DC battery it has overcharge protection and 3 zone charge strategy. We are also not sure what the amp of the charging should be as long as it charges within 5-8 hours. We have a two battery 12v, 7AH, 6cells each. with a standby use of 13.5-13.8v initial current 0.1c, cyclic use 14.1-14.4v 0.25C max each.
we would really appreciate if u can guide us in the right direction.

 

I simulated the circuit, and while I could get it to work, it really didn't look very promising.

Q5 is used as a voltage clamp; once the battery reaches the terminal voltage, Q5 starts dissipating a LOT of power as heat. It might be OK as a trickle charger if you use a low VA power source, but the more power you put in, the hotter Q5 will get once the battery is charged.

I don't see how this charge controller has a 3 zone strategy. Perhaps you can provide a link to where you obtained the schematic in the first place?

Also, unless a small capacitor is added between the gate of Q5 and ground, it will oscillate during the time it starts to clamp the input supply voltage.