A 100 Ah 12V battery is a fairly common specification for a deep cycle battery used for camping purposes.
For the benefit of a large userbase, this specific battery can be used as a reference point for our estimates in terms of how long the battery would last with the common electrical appliances found on a camping trip.
For the sake of simplicity, we would take 3 devices, namely a TV, a fridge and laptop (charging).
First, there are certain points to consider that may skew the results of our calculations. The battery is not 100% efficient and there are other non-idealities at play as well.
The charge level and the age of the battery are also valid considerations. If the battery is not fully charged and it has started to lose its charge holding capacity due to its age, then the results may not reflect the ground situation.
Assuming after the necessary adjustments, the battery can provide 80 Amperes for 1 hour. The current assumptions, after ignoring the starting current, can be taken as: TV (5A), Fridge (4A) and Laptop charging (1A).
This means that the battery needs to provide a total current of 10A. Considering the battery capacity, this means that if all 3 of these electronics are used simultaneously then the battery would last for around 8 hours.
However, this is usually not the case, a TV may be used for 5 hours, a laptop may be charged for an hour while the fridge compressor may only run for 12 out of every 24 hours of each day.
This can increase the time a battery can last drastically and can reach around 2 days or more if the use of appliances is infrequent.