Normally, the 24 volts battery will be formed by 2 - 12 volts battery.
Please detail how the 24 Volts is physically built.
I have seen some UPS that have 24 Volts that under good "examination" were formed by two 12 volts batteries, also, some 48 volts with 2 - 24 volts banks with true 2 - 12 volts batteries.
If indeed you have a true 24 volts single body battery and you need to have 12 volts only, I would suggest to have a PWM = Pulse Width Modulated, voltage regulator to produce the 12 volts, or if the bank has a 12 Volts borne then with a 24-to-12 volts equalizer, you could load and charge the lower 12 volts, so when loading, the equalizer will bring power from the upper 12 volts battery to the lower battery and when charging the lower battery, the equalizer will charge the upper battery, "Pricy" converter though.
Regards
Nando