When you're pulling an unbalanced load off a 24V system, I would definitely rotate the batteries now and then. The problem is going to be charging - say you have one battery at 60% and the other at 80% SOC - and charge them at 24 volt at say 30 volts for absorb. While the system voltage will be 30, the one that's lower on SOC will lag behind on bulk at say 28 volts, and that's going to run the other one 32 volts.
So keep tabs on the individual voltages of the batteries so you don't over-boil the one that's higher on SOC and run it out of water.
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Chris