OP here - I call PD and they said to suspect the battery. I pulled it out and I will take it up to Interstate as soon as I can.
If it's the battery, I have had nothing but trouble with Interstates, although most everyone claims they're good batteries. I have had 2 go bad on my 4-wheeler, and this trailer battery had a bad cell from the get-go brand new, and I didn't realize it until on the road to Alaska last Spring (2012). An Interstate dealer in Montana replaced it at no charge, and this current battery is the replacement.
Arghhh...
I am now going to Google how to check the water on a battery...isn't that stuff acid?
