That's enough power to run my relays or strobes in fire alarm . While .55 ma is very low it is enough over time to bring voltage from 13.2 to sub 12 vdc ,and at this point not enough voltage/ amps to crank the starter motor under load@c10 0.55mA is less than a fifth of the maximum leakage allowed thus why would it be a drain? Unless the decimal in the reported number is off.
Forgive my mistake. Hence why I do not do battery calculations these days .I googled fire strobe specs. I suspect your strobe is operating in the range of 50 mA, or one hundred times his posted measurement.