UPS Required

The important things to specify in a DC UPS is the amount of time you want to maintain the load. You have now said 1 hour.

The other thing is that batteries are usually rated at the 10 hour rate. Therefore a 30 Amp Hour (AH) battery should give 3 amp for 10 hours.

At 30 Amp you will probably need about 45 AH minimum and I would go for about 60 AH to be sure you get your 30 A for an hour.

Also be aware that most DC UPS units run at the charging voltage of the battery around 28.8 V and when the main power fails go straight to the battery nominal voltage of just over 24 V. This will drop during the 1 hour at 30 A to about 22 V which is the lowest that the battery should be run down to. After that the unit should cut the supply to the load to avoid ruining the battery by running it down to very low voltage.

Can your application handle this voltage variation?

If you need to remain at 24 V +/- a small variation you need a unit with a regulated output during the normal running when the mains power is available. It is possible but quite expensive to also have a regulated output while the mains is unavaiable but this needs a DC - DC converter with a regulated output to step it up from the reduced battery voltage.

A final thing to remember is the recharge time after running the battery completely down to its minimum. Frequently this is in excess of 24 hours. If your power supply is too unreliable then you may suffer if there is a second interruption.