Battery or alternator

Measure the battery voltage with an inexpensive digital voltmeter while the engine is running. It must be between 13.75 and 14.75 volts. If it is, suspect a defective battery or a drain on the system.

Battery voltage is measuring ok any ideas what could be draining it.?

Very hard to tell when there is a drain. Dozens of common sense functions have been replaced with very trouble-prone computers to provide the toys and gimmicks people demand. Some of those computers have to "time-out" and go to "sleep mode". That can take up to 20 minutes during which time they can draw up to three amps. There is a special procedure to insert an amp meter in series with one of the battery cables to measure the drain. If anything is done to break that connection, including simply switching the range on the meter, that time-out sequence starts all over. What you can do is look for things that haven't turned off after 20 minutes. if the engine starts after sitting a full day but not after two days, that would be typical of a small glove box light staying on. Most computers will draw more current when turned on and will kill a battery overnight. Look for add-on items such as a cell phone charger or aftermarket radio that is wired incorrectly.