All TTs are very similar. What model Jay Feather do you have? You may get more specific answers. How long have you had this TT? Are you connected to shore power or just using the battery?
You have two separate power systems in your TT. You have your traditional residential 120 volt , in which you need your shore power cord plugged in to make that system work. When plugged in on 120 Volts, all your basic outlets, microwave, AC, and to charge your battery will work. The other system is you 12 volt DC system, just like a car. It uses your deep cycle battery to power your devices, such as lights, bathroom exhaust fan, furnace, refrigerator (controls), radio, gas/carbon monoxide detector, and your slide out motor. Just sitting in the driveway, not connected to shore power, there are a number of 12 volt parasite power drains on your batter, such as the gas/carbon monoxide detector. While just sitting within about 2 weeks these parasites will drain a fully charged battery. So you need to stay plugged in or disconnect the battery, when in storage.
A 12 year old TT, may just have a worn out dead battery that needs to be replaced. If the TT has been sitting unused, untethered to the shore power, you may have drained the battery.
With a little more info, I bet we can find the root issue.