I have 18 dollars in my Blizzard account. If I buy a 20 gift card and add that, i will have 38 $ in my account. Would I be able to buy 60 days worth of time with that? Or do i need to buy the proper 60 day game card?
You can buy game time from the shop with battle.net balance. (But not a subscription.) You do need to have the full amount including tax as it won’t let you split between payment methods. $38 should do it anywhere in the US, outside of that I don’t know the math.