What is the best way to keep a Titan if you are not going to drive it for a long period. The battery keeps needing charged when we go to start it after a few months and the battery is not that old.

Start your automobile every few weeks and leave it run it'll charge the battery and keep everything good😎👍🏽

You didn't say what year your Titan was but even the original Titan's had airbags and keyless entry available. Those systems remain ready to engage at a moments notice and use the battery to keep the vehicle in a ready state. Even more so if a remote start system has been added. Typically the best way to maintain a battery for a long absence would be to disconnect the battery and keep it on a battery minder.