Calculate run time of backup battery

This is what I am using for backup for my computer.

Expert Power EXP 12180 12 volts 18 amp hours

My Xfinity modem uses 22 watts.
LG monitor 60 watts
Computer 55 watts
Grand total of power usage is 137 watts.

Is there a calculation that will show how many hours my computer will run using the backup battery?


12 Volts x 18 amp hours = 216 Watt-Hours

216 Watt-Hours / 137 Watts = 1.57 Hours.

This of course is the rough number. Depends on how bright the monitor is, is the computer at idle or doing productive work, etc.

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Thanks Patreons. I measured the values using a Watt-O-Meter.