Not all camping sites are blessed with a proper power supply. In some cases, it is irregular while in other cases, it is absent altogether.
This gives rise to the concept of dry camping where the deep cycle battery is charged beforehand with the assumption that there may be no power available to recharge it.
This naturally leads to the question of how long the battery would last. This can be approached from different perspectives.
One way to see it is understanding that this is a fairly subjective question. It depends on factors like the ratings of the deep cycle battery and the loads. This gives a ballpark figure as to how long the battery would last while powering the electrical appliances.
For refining the estimates further, allowances for inefficiencies in the battery and other non-idealities need to be factored in as well.
After gathering the relevant data and taking the necessary assumptions, a few basic calculations can be done. If done correctly, the resulting estimate is fairly accurate.
The other option is to consider the averages of general data available in the battery industry. It is estimated that a deep cycle battery can last around 2-3 days while dry camping.
These estimates are based on considering things like laptops, camping fridges, TV's and other popular camping electronics as possible loads and the usual size of the camping batteries.
The purpose of doing so is to provide a general idea of how long the battery could last. For more accurate estimates in accordance to given situation, the previous calculation-based approach needs to be adopted.