Luminous RC18000 (150Ah) full charge Battery 400 watts bulb load around 3 hours 10 minutes backup it will come.
You also Calculate battery backup in your self, battery backup formula is = Battery Ah * 12 * Number of Battery * Battery Efficiency / total load in watts.
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It also depend on the usage of the battery and appliance of load on it. If the load or appliance wattage is reduced the backup will improve.