Hi want2work209. Welcome to the forum. 13.5 volts is not ideal but it should be enough to charge the battery enough to start the engine. You might find the voltage creeping up as the battery becomes charged. It should be between 13.75 and 14.75 volts.
If you can drive all day with no problems, then the battery is dead the next morning, look for something not turning off and draining the battery. A glove box light, trunk light, vanity mirror light, and cell phone charger are common causes.
Sunday, July 4th, 2010 AT 3:41 PM