It seems like you might be dealing with either a weak battery or a charging problem. Have you had a chance to check the voltage? It should be about 12.6V when it's off and between 13.5 and 14.5V while running.
It's also a good idea to take a look at your grounds and connections, loose or dirty terminals can drain the charge pretty fast.
By the way, how old is the battery? If it's not holding a charge after you've fully charged it, it could be time for a replacement. Would you like a quick guide on how to test it?
