what is easiest way to find out if it is a battery or alternator

With your vehicle running, disconnect the POSITIVE terminal of your battery. If your engine cuts off, your problem will most likely be the ALTERNATOR. Also...the alternator is what powers the battery. It charges the battery when it's running, therefore...another easy test is to do this....if the interior and dash lights come on really bright, but then slowly dim, then it indicates your alternator is the culprit. It means that the alternator is NOT feeding your battery because it's not keeping a charge when you're running it. Good luck!

From the sound of things , a professional (shop) might be a good idea....////..... Go ahead with #2 suggestion .....but be very careful...1 good voltage spike could take out a lot more than the alternator!