Pretty sure it's the altenator but my charge voltage is low some times and some times not. Will go way low if i let it idle for longer than a min or two and the battery is sluggish on starting

 

Before you replace the alt. check that the belt is tight enough. Mine did something similiar to this and the belt needed tightening ( I went ahead and replaced mine). Might work,might not, but it is worth a try.

 

Would totally agree with Drakan1908’s suggestion – also check the electrical plug connection to the alternator. Unplug, give the contacts a spray with WD40 (or similar) and firmly re-connect the plug to ensure a good electrical connection.

Before spending money on a replacement altenator, check the battery charging voltage with a meter, rather than relying on the gauge in the instrument panel.