I order most of my
batteries from lighthound....Which seeing as how the Old Goat's are primarily a 14500 I'd suggest these...
AW 14500 Protected Rechargeable Lithium Battery
Unless you have the newer 5v which I believe takes 14250 batteries which can be located at the same place. You can buy cheaper 14500 batteries but the AWs are incredible, last forever it seems, and provides a unique
vaping experience in that they seem to retain their voltage for much longer. You'll also need an appropriate battery charger which can be found there as well.
Drip tips or mouth pieces are a dime a dozen depending on your preferences. However, since you have a box mod and a bottom feeder it might be in your best interest to get one. I'm fond of the stainless steel t-tips from SuperT as well as the Cherry Vape tips from Clouds of vapor. Also? If you want to try something a little different, hit Avid Vapor or Ikenvape for their 306 LR atomizers. They thread similarly to the 510 so you should have no problems if you choose to go that route.