Hi awboatguy,
Welcome to the Heartland Owners Forum.
If you mean that the battery dies while the trailer is in storage, not plugged into shore power, it's because of small parasitic loads in the trailer. These might include a radio, alarm(s) and perhaps other devices that are never completely off.
Your trailer may not have come with a battery cutoff switch. If that's the case, you should add one. They're relatively inexpensive and you can probably get one from your dealer parts department.