Watt Hour Capacity of 27 Deep Cycle battery

All that really matters is the AH rating. You can go here to take a look at what you can run for what length of time. If you are drawing 100amps (not what a TV draws these days but might be a good combined usage number) you would be able to run 4.7 hours to complete discharge. However, you never want to do that and a 50% SOC is generally considered the correct time to recharge. That leaves you with only about 2.5 hours usage at that rate. Take another 5-10% loss due to inverter inefficiencies and you are down to about 2 hours.
http://ep.yimg.com/ty/cdn/sports-imports/BatterydrainCalc.html