Switch Out Battery Car Battery

Can you switch out your car battery for a deep cycle battery and used it as your power source?

Vehicular starter batteries are designed for very shallow discharges, typically 5% capacity or less on each start.

So yes, you could pull it and use it as a power source, but since they are not designed for deep discharge, you'll simply use up it's useful life quicker, especially if you discharge more than 10% or so on each cycle.

Success at replacing starter batteries with deep cycle batteries will depend upon the idiosyncrises of the specific vehicle. For example, many modern vehicles have "smart alternators" that purposely hold the battery at a low charge, so that the alternator can be used for braking (saves fuel). Such a vehicle would not be a good candidate for what you propose. On the other hand, your idea could work on a vehicle with a simple charging system.